Oh, they are bots for sure and are trying out your subreddit, no doubt!
Most of the posters' account are either created on Sep 17 or 18. That can't be simply a coincidence!
But I guess the reason they are posting on your sub is, they want to increase the activity of the account by posting regularly on different subs [mostly crypto & stocks related subs], follow the game the Reddit policies and finally, when they are ready, they will go haywire and attack the larger subs.
Just saying, you know!
:P