> When someone tells you something relies on UDP, nobody in their right mind assumes that this person implemented TCP features on top.

AFAIK it's rather common in multiplayer games to do TCP-like features over UDP, as they usually need the UDP features but also need reliable transport for some data, and it's rather tricky to do both UDP and TCP at the same time.

See for example https://fabiensanglard.net/quakeSource/quakeSourceNetWork.ph... or https://gafferongames.com/post/reliability_ordering_and_cong...