よろしくおねがいします can mean many things in different contexts.

The phrase is often first learned as a component of introductions, and thus may be translated as "pleased to meet you" or "how do you do?" but its literal translation is "please [treat me] well/favorably."

Outside of introductions you'll often hear it:

When starting a new project with someone: "Please be a good teammate to me."

When you've agreed to help someone or do them a favor: "Thanks, and please help me like you promised."

When you're about to start playing a game with someone: "Please don't cheat." :)

Did you agree to help your colleague with something during dinner? That might account for it.