He could have a legit copy of Vista and an upgrade disk to 7 ultimate which he got cheap, by using a student deal or similar. There are ways of doing it legitimately for not much money.
OS: Windows 10 64 bit Professional
CPU: AMD Ryzen 5900X
RAM: 48GB
GPU: Radeon 7800 XT
CPU: AMD Ryzen 5900X
RAM: 48GB
GPU: Radeon 7800 XT