How can you be sure it wasn't a lag spike (on his side) ?
I happens sometimes to me because my ISP is trash.

Actually that bug seems to be happening for a few time.
People can randomly respawn in Clash.
Some can even spawn right after joining the server mid-round.
Apparently, you can "force" the respawn my using the "auto-respawn" option and spamming M1 when you die. This info was not verified, though.

I must agree that this game should have stayed in beta for a few time. Also a lot of players are complaining (and I think you saw it in the Steam reviews) that in order to be a competitive game, you should provide the same options to each players, and a lot of them don't like "grinding" to get the weapons.
Also, until a competitive gamemode with maybe a matchmating system, the end-game will be pretty boring and you risk to lose a lot of the playerbase.