This was for a non-commercial hobby project and there was no actual development involved. Even if using a Windows VM in that way violated some Microsoft licens

This was for a non-commercial hobby project and there was no actual development involved. Even if using a Windows VM in that way violated some Microsoft license, I don't think I'd care much. It's not like Microsoft is gonna sue an individual using one of their VMs for an hour over some licensing technicality. I'm sure they'd care if this was in a commercial setting (and then I'd actually care about the license), but for personal, non-commercial use, I don't see it. Worst case scenario I'd actually buy a Windows license. At least for me, this is more about the technical ability to run an OS in a VM than about the legal details behind it.