Image copyright Instagram: Anthony Bourdain Image caption This photo, shared on Instagram by US celebrity chef Anthony Bourdain, drew more than 120,000 likes and thousands of comments

Deep in the heart of Hanoi, US President Barack Obama sat down for a $6 meal with celebrity chef Anthony Bourdain on Tuesday. The chef, known for his love of adventurous street food, described the date in a series of tweets and an Instagram post.

Here are six observations about the noodle summit at a hole-in-the-wall eatery.

1. Nobody appears to know they are there

The other diners appear to be totally oblivious to the presence of the US president, a celebrity chef, and presumably a substantial security detail, photographers and film crew.

"Love how the diners were so good at pretending they had no idea who is sitting at the table next to them," tweeted Brazilian journalist Sofia Perpetua.

The crowd outside the restaurant was slightly less restrained.

Image copyright EPA Image caption The scene outside the restaurant that greeted the US president

The discussion on Reddit, which attracted 3,000 users, spilled over into where any secret service agents might be hiding.

2. The symmetrical food

On the menu was bun cha, a Vietnamese dish of grilled pork and rice noodles, some greens, all washed down with Hanoi beer. On social media, there were questions about the positioning of the food.

Image copyright Instagram: Anthony Bourdain Image caption They'd like to teach the world to eat in perfect symmetry

"The perfect alignment of the food disturbs me," said an Instagram user. "Look at how symmetrical the bowls, chopsticks and plates are."

A bit more joie de vivre from another user: "Eating in perfect symmetry, awesome and smart."

3. Presidential chopstick skills - but a wrapper on the floor

Anthony Bourdain was quick to praise the president's chopsticks skills, describing them as "on point". And everyone seemed to agree.

"Proud of the president, that he placed his chopsticks neatly on top of his bowl and not stabbed them into the noodles - that would have been so rude and a big sign of disrespect," said another user.

Image copyright Twitter: Anthony Bourdain Image caption While many praised the US leader's chopsticks etiquette, one user pointed out the appearance of a wrapper under the table

A photo from a different angle irritated another Twitter user. "Is it just me or does anyone not realise how a red chopstick wrapper has been dropped on the floor? Taking points away from him."

4. Plastic stools and Hanoi beer

The unpicking of the details in the picture became about the Vietnamese things in life.

"Ah, our rickety blue plastic stools - that's Vietnam for you," said Instagram user Chi Mai.

Media playback is unsupported on your device Media caption The BBC's Jonathan Head samples the noodle dish President Obama ate in Vietnam

"No fancy interior, just simple furniture to let the food and conversation do the talking," said another.

Others wanted to know the US leader's choice of brew.

Question: "What kind of beer did they drink," asked Mic Vo on Twitter.

Answer: "Don't disappoint me, hope they had Bia Ha Noi," said another user.

5. The talk over noodles

Another question that boggled the minds of social media users: What could the world's most famous TV chef and one of the world's most powerful leaders be talking about?

Speculation ranged from Donald Trump to food to curing cancer, achieving world peace and finding unicorns.

Image copyright AP Image caption Many social media users were questioning the setting up of the photo on Mr Bourdain's account

We don't know how long the meal even lasted. Some accomplished foodies could polish off a meal like that in less than 10 minutes.

Perhaps they spoke about the fact that the president had just lifted the US arms embargo on Vietnam.

6. So what was the photo really for?

Mr Obama found time to sit down for dinner just hours after his announcement about the embargo. Others on social media, saw it as publicity for Bourdain's food show.

How much did they plan it," asked Instagram user FlyMy90. "Were they filming for an episode of Bourdain's show?"

"Dinner will air in September," the White House was quoted as saying by one journalist.

Despite the speculation about the staging, the picture still delighted many around the world.

"Think you're cool? You'll never be eating noodles, drinking beer and sitting on low plastic chairs while talking to Anthony Bourdain and Barack Obama in Vietnam-cool," tweeted New York resident Jon Hopper.

Reporting by the BBC's Heather Chen.