Windows 10 won't attempt to install unless it has enough space to complete, and they look for 16 GB.
So what I suspect actually occurred is that your hypervisor was set up to misreport how much space as available to Windows, so Windows 10 tried to install on the space it thought it had, only to hit the wall on the "real" filesystem below.
It is unlikely this ever would have occurred to anyone else in your family, unless they're running Windows in a hypervisor that misreports space.
This was not under a hypervisor, but it did happen as the same time as I was installing some large pieces of software; I'd just recently reinstalled, and was looking forward to playing X-COM 2.
The 3GB number is how much space was free after I excised the broken shards of the Windows 10 installer. So, sure, the space probably got taken up after the installer checked if there was enough, but it's not like I ever told it to start running.
One would think so, but then one would also think that nobody would ever design a boot recovery procedure such that it has an error case where it deletes all (several hundreds) executable files on the disk, completely hosing the system. But Microsoft still managed to do the latter. It's likely not that nobody thought about it, but maybe not the right person, and in big companies that can matter a lot.
They didn't seem to think of the possibility that I might have a long running, important process on a machine that I am not physically at. Restarting a machine just because I am not there to say no is bad.
So what I suspect actually occurred is that your hypervisor was set up to misreport how much space as available to Windows, so Windows 10 tried to install on the space it thought it had, only to hit the wall on the "real" filesystem below.
It is unlikely this ever would have occurred to anyone else in your family, unless they're running Windows in a hypervisor that misreports space.