The downturn in global markets on Tuesday over concerns about Italy's political power struggle and the possible economic fallout as a result highlights the mistaken assumption that the world was in a phase of synchronized growth, economist Mohamed El-Erian told CNBC on Tuesday.

"The mistake people made is to confuse a coincidence of a pick up in growth around the world with something that had legs," Allianz's chief economic advisor said in a "Squawk Box" interview. "We were just in a lucky coincidence."

"People are now realizing the only economy with real legs to it was the U.S. economy," said El-Erian, formerly CEO of bond giant Pimco.

In 2017, the U.S. stock market was roaring based on a number of different influences, according to El-Erian. "The U.S. was policy-led, deregulation, tax cuts. Europe [was] just in a natural healing process," he said, while "developing countries were bouncing back" and China was in for a "soft landing."

After hitting an all-time high on Jan. 26, the Dow Jones industrial average tanked in early February. The catalyst at the time was a higher-than-expected wage number in January's jobs report sparking fears of inflation and interest rates rising more aggressively than projected.

Stocks on a closing basis eventually bottomed out on Feb. 8, briefly plunging in and out of 10 percent correction territory. Since then, the Dow has recovered, closing Friday about 7 percent away from its January record.

El-Erian predicted Tuesday that if Congress manages to pass an infrastructure bill, then the U.S. economy could break above 3 percent GDP growth. He expects 2.5 to 3 percent growth this year.

"We've had deregulation, we've had tax cuts — whether you like it or not it does boost growth," he said. "If we can just get the infrastructure done, then the U.S. will break into a higher growth."

The Commerce Department reported last month that U.S. economic growth slowed in the first quarter, advancing at a 2.3 percent annual rate. However, GDP in the first three months of the year tends to be sluggish because of seasonal quirks.

Regarding the Federal Reserve, El-Erian said the Jerome Powell-led central bank has done well so far but urged the Fed to only implement three interest rate hikes this year. "The market has priced that in. We have transitioned to that regime without major breakage," he said.