Yes. Google.
All apps from which Google does not make any $ are flagged. This I have observed by numerous posts of members whose apps are removed and they were simple ones with no ads.
I think if B4A Bridge shows ad, which helps Google make $, then it will be not flagged.
I highly doubt this is correct.
I also don't get a warning when I start B4A Bridge, so it's not a general warning. Instead I suspect the manufacturer of your phone have their own antivirus solution that produce this false positive. (In theory it could be you that installed an antivirus on your phone, but you would know if you did that, I suspect.)
Lastly, the wording in that message doesn't even remotely sound like a message from Google.