Our 2 ~80 year old chinese chestnuts have started dropping this week but it's going to be a very bad year. Not sure what happened, but tons off the burs fell of before developing and strong wind took more
I have some falling and some that haven't started. Nearly all of my chestnuts look about the same size as yours, but I have one tree just starting to bear that made some that are bigger than normal. To the best of my knowledge it is just a run of the mill Chinese seedling.
Of the 2 old chinese chestnuts in my yard, one has large nuts like in your top pics, while the other has smaller that look like your lower picture. I know there's quite a few bred varieties of chinese chestnuts, potentially this is the reason.