The first Ethernet was on coax yes. It was also a shared physical bus so the 10 megabit was often shared among a room full of computers. Despite this it felt speedy!!

But times have changed a lot. In those days there was more focus on collision detection and avoidance which is no longer relevant with today's switches.

Ps it was not the same coax as for TV. TV coax has 75 ohms impedance. Ethernet (and most radio equipment) uses 50 ohms. It was annoying not being able to those cable TV stuff but handy for me as a radio amateur to be able to use the same cables.