Random Stealth Updates?

So I was playing both of my accounts last night, and I disconnected on one account. I tried to log back in and it got stuck at retrieving character list.

I had to completely close the Bnet launcher, and upon launching it I got a 347mb update.

This whole time my other account was still logged in and everything was normal in game.

Does this happen to anyone else? I’m also curious if anyone knows why?