Edit: I've been clear about my reasoning; you have just resorted to ad hominem attacks on my understanding or emotional intelligence. If you don't have any actual counterargument, I'll consider the debate to be over.
On the merits--human babies are hard-wired to recognize faces from birth: https://news.stanford.edu/news/2012/december/infants-process....
How does a baby express being upset? They can smile on purpose at 2 months: https://www.uofmhealth.org/health-library/ue5463. So the lack of a smile is a detectable sign. After just a few weeks, they have a range of reactions short of crying. They change their facial expressions based on what they're feeling. They make grunting noises to express minor discomfort. You can even tell when they're bored.
It is if, as the other comment did, you just claim I don't know what I'm talking about without providing evidence of that.
But congratulations to you on using sources and arguments. I still think you're projecting. In my experience babies have no trouble recognizing human faces with masks on because they are drawn to eyes. In fact, they even recognize and will respond to a smile behind a mask, again because the muscles around the eyes contract. Probably masks are harder for slightly older children who are learning language, because they can't associate mouth movements with sounds.
How can a two month old possibly express that he's "weirded out" by a mask. As you said, you were on a plane, which was surely a novel situation for him, so even if he was behaving strangely you can't know that it was because of the mask. I think it's much more likely you're projecting your own fears onto him.