You are good with all of your 25 accounts because none are from the same casino, thus not multi-acc, and most importantly, you're probably doesn't have a prior with the provider. The OP though, arbing at one point, and I am quite sure they have the record of it. Thus, you can't compare your situation with his. It's like going through the airport where your name is not on the watchlist, while he has an interpol-issued warrant.
I hope that helps you understand the difference and the situation here.
It doesn't matter which casino he is using ,either that's a different one or the same one.
BetBy is causing him most issues and much less the casino itself.
If he is registered on 10casinos that all use BetBy as their sportsbook provider ,then said provider could cause him issues if they feel like it (causing him issues is not legal of course on the part of BetBy , but since there are no regulators to slap them for such abusive action , they can do as they please.)
I have had accounts on many casinos blocked without any action simply because the registered email was the same as the one I had registered and used on another casino with the same oddsprovider behind so they can do this if they want to.
Of course I had accounts that didn't face any issues , but using different emails and IPs is not a bad approach based on my experience.
I had also encountered one betby casino that when you register you have to "check" (like you agree) to the following statement :"I accept that I will not use and have not used in the past any similar betting platforms".Sadly I didn't take a screenshot of it , or If I have I can't find it right now.
Of course I ended up not registering there , but to me that looks like a message from the BetBy provider to the bettors using the sportsbook.