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.
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