They were using FTDI's USB VID. Probably most of them also were marked as "FTDI" on the chip package, but of course that's not what FTDI's drivers looked at.
What FTDI did, on the other hand, is malware and clearly illegal. It is destroying private property and I guarantee violated multiple laws in many countries.
Of course this kind of vigilante justice by FDTI is illegal, but who is going to press charges if that means they will get their devices taken from them and destroyed?