To my ear "oh cool, today is the day you get to learn about X." is even more patronizing than the feigned surprise. Feigned surprise may have a tone of superiority, but at least it means they respect my knowledge enough to be surprised that I don't know.
YMMV, but I find this has more to do with the attitudes of the participants. Knowledge is not a zero-sum game, I hope to learn new things every day, and want the people I work with to help level me up. If someone wants to take the time to share their knowledge with me, I win.
If it was being said passively aggressively, I would agree with you (and perhaps you've mainly experienced this interaction that way).
"oh, you're not familiar with X? it's actually pretty cool. it has benefits Y in situations like Z, which might be useful to you here because [...] I'll send you some links to the resources I used to learn about it. ”
