Did something change with the arena games matchmaking?

For the 1st time ever instead of joining a game directly i ended up in a lobby, without the option of declining the game (returning to the idle page showed 'arena in progress', wich took me to the lobby.
The opponent was a low level account, and it took a long time for the game to start. he than proceeded to get booted from the game for being afk.
how does it work, does the opponent auto join after some time in the lobby or something like that?
why couldnt i leave the lobby?

do i have to expect to see the lobby page for next time too?

This happened because you had color superiority (higher level) over the opponent and claimed their only color because they had no secondary color set. They had to click Join and select their secondary color to join the game.

Iirc the lobby expires after some (generous) time.

Edited 2/7/2022 11:50:25

it should expire after boot time (iirc), at which point your opponent will get a random color and get force joined into the game