Oh, hey; look at that. I’m guessing that the difference is in its source of creation. Mail comes from NeXTSTEP while Notes comes from iPhone OS. One was designed back in the days of “have a ton of separate windows open” and the other in the “no windows, ever” phase.
I’m almost certain he’s joking, particularly since he mentioned two people who’ve explained this in the past. Really have to throw an ¡ or /s on these things, Frosty. No matter how outlandish the belief, someone here will hold it.