It might me. But in academia there is a lot pressure and many people decide to work on weekends, some have to work on weekends (e.g. long running experiments that require human input every 6 hours), and some are forced to work and only if there is an abundance of other forms of abuse it might get exposed.
Consider famous case of https://www.swissinfo.ch/eng/technology-institute_prestigiou...
If you read the detailed postmortem it is clear people were working way beyond normal working week. And it's not even mentioned as one of problems about the work with this professor.
