Black goes from having 43.4 seconds to 43.5 seconds after playing the almost certainly premoved hideous blunder of 13... Qxg2. It shouldn't be possible to gain back time in a game without increment unless I'm fundamentally misunderstanding something here. I suspect this is either due to the fact that lichess attempts to refund time based on ping or it's a rounding or floating point error. Either way I think it qualifies as a bug. I've seen similar things happen before, but never with saved game meaning it was likely only a clientside visual error in those cases.
It may be related to the bug that occurs here: lichess.org/Quls1Dpg where the clock shows black as having 30 seconds until black makes his first move despite the fact that black did not berserk in this 1+0 game. That one is almost certainly just a visual error, and I am unsure if it appeared that way to the players or whether this bug merely appears when looking at the clocks during playback of the game.