That is very strange. I've just spent 15 minutes trying to come up with some kind of educated guess, but I can't think why OOTP would create players out of the blue. It can't be a situation where a team didn't have enough players to field a team. You would have noticed an organization with only 7 defensive players, obviously. Oh yeah, I just remembered that you do have minor league teams too, so it can't be due to a shortage of any kind. Honestly, I really can't think of a reason that would have happened to your league. You might want to ask in the OOTP 21 General Discussion forum. One of the OOTP Veterans must know the answer...and if not, there's a good chance a developer will pop in with an explanation.
Two Rookies win Batter's of the Month (AL & NL)? Wow. Might have to keep an eye on them next season. Both league Champions seemed to have a pressure free end of the season. Hopefully, next year will supply us with a little more drama down the stretch.
How do you have Trade Frequency set in your league? I'm just curious if you like seeing more or less trading over the course of a season. The AI will offer me a 2-star 30-year-old for a 3-star 20-year-old and a 3.5-star 24-year-old - or even more ridiculous - whereas, I often see some very fair, interesting trades when it's AI & AI trading in my league. I know that's not unique to my league.