There is an assumption not to be an asshole. But that's where it ends. If an endless stream if cars likes your directions, they can't expect you to keep standing where you are, giving each of them directions.

In the same way, if someone posts some code you can file a bug or give a patch, but that doesn't entitle you to anything from the original author. Maybe you helped him making the code better and you're scratching each other's back. Maybe the author is just extra nice to you. But just because you've received a gift, you're not entitled to more gifts.