I have recently inquried toward a few Japanese friends, and some of my wife's friends, about the four season issue. I explained to my wife why I feel irritated at this question, and she also knows that most Western countries have four seasons. So we discussed, me, her, and two friends about it a few days ago, and the three of them admitted that they were taught at school that only Japan had four seasons. A few people have contested this on this forum, saying that children are taught that most countries around the world do not have as distinct seasons as Japan. However, my wife and our two friends were sure that, in their case, they were not told that Japan has more distinct seasons, but that only Japan had four season and that's it. I asked whether they were taught that in geography class, but the three of them said it was in "kokugo" (Japanese language) class sometime in the early years of primary/elementary school (they also said "chichai koro kara iwareteiru" => "we were told this since we were little"). All three went to different schools, by the way.
I've never taught like that only Japan had four seasons.
Maybe they only hesited to say that they were indifferent to geography. I forgot many math formulas I learned. In that sense, I can share your friends' feelings.

A bit off-topic, but when your wife has the same critical mindset as yours, it would be very nice of you to start a thread about Japanese education and the J Teacher's Union or 日教組.