This is good, it means he's converting his food into growth and energy.
Also I'll give you fair warning, at some point while you're assist feeding that food response may kick in and he'll grab one of your fingers. I had a BRB baby do that. Fortunately they have small teeth when they're babies.
Right now I would love that this little guy has had me so worried I would gladly take getting bit if it ment he was trying to feed