This did happen to me once. I did once comment that code of one of mods was fact wrong (code snippet). The mod warned me about banning me from the sub. I just requested please see the code and you did type it incorrectly. Next day ban...
Admins are employees of reddit who can ban you globaly from the whole website.
Mods are "random" people who created a subreddit or happen to moderate it. They are unpaid volunteers and can only ban you from the subreddit they moderate.
There is lots of drama about people trading mod spots (there is that person/group of persons who modereated like 250 subreddits), hacking someone to become head mod - and then using a sub to push agenda, or straight out selling mod spots. You can earn a suprising big amount of money if you mod certain subreddits (e.g. related to cryptocurrencies or news).
Reddit admins seem to not care at all who mods ban. Some time ago they introduced a process to remove mods who dont moderate a sub at all (remove illegal/against TOS conent) but that's that. If you are a mod you are a king of a sub, only other mod (of same subreddit, who was there ealier) can remove you. In theory admins could but they dont care, unless they have bad press.
That's why there are many "splinter" subreddits with similar names.
Complaining about top reddit admins will get you banned for targeted harassment as well.
They can do whatever they want since it's their site. I just don't think I'm interested in engaging when I can setup my own blog.