Not at all. I wonder where you got this definition from.
A beta is just unfinished, but mostly functional and lacking features. I can be bugfree already. The DooM betas from Mid to End 1993 work all fine. No sound effects, no lighting, no animation but no real crashes. These are, by definition, betas.
It's probably "laggy" (which is also weird since it's nothing that could slow down much, it's not calculating CAD graphics or Bitcoins via CPU, it's basically just a frontend, a GUI that hands over stuff to the actual game client) but both is just poor for such a company like RIOT Games.
A beta phase for a cheap GUI frontend. No beta for the game. Just. The. Client.