uuidgen comes from libuuid, which is part of e2fsprogs
The manual page for the e2fsprogs uuid_generate functtion states:
The uuid will be generated based on high-quality randomness
from /dev/urandom, if available. If it is not available, then
uuid_generate will use an alternative algorithm which uses the
current time, the local ethernet MAC address (if available), and random
data generated using a pseudo-random generator.