A game auto-resigned while Lichess reconected?

I was playing this game a few moments ago. I had a completely won position with a full rook up on a simple endgame. I was in my notebook. At a point, Lichess said "Reconecting" on the bottom-left of the screen. I waited a minute or so, and since it didn't leave I went to my PC and open Lichess there. The game displayed that I had resigned; I lost elo because of this, but even worse I lost a game that I had completely won because Lichess thought it was a good idea to resign on my behalf? What happened? Is this a bug?

It says white left the game not that you resigned. If you leave the game for a specific amount of time you automatically lose

How long is the specific time for LIchess to give you the game as lost?

It's a good question, for I could swear not more than a minute and something went by. At the same time, when I entered the game it said White resigned, but now it does say that white left the game, as TrappedPiece pointed out.