Sounds like he was upsetting his neighbour on a regular basis to the extent that the neighbour filed a complaint. Yes, if you're making noisy zoom calls at unsociable hours in a studio apartment with thin walls you're going to get in trouble. If he'd been discreet and not caused trouble for people around him he'd most certainly have been left alone like many others are.
From an interview a few years ago with the Chiang Mai Work Permit Office:
4. A foreigner sits in his apartment in Chiang Mai and teaches Chinese students online via Skype.
The verdict: " Officially, work, however it is not a main concern to our office now, so we allow the foreigner to do this without a work permit. "
This verdict considers the scale of the work and the environment.
https://www.chiangmailocator.com/wiki-can-digital-nomads-legally-work-in-thailand-p177