But it changed within a second... They can be out of tone within 1 second? Is that possible?
Well, yes, in theory. The string is being held in place at two ends, the tuning pegs and the bridge. In this case the bridge is a tremolo unit. If one of the springs in the tremolo unit snapped for example then the tension on ALL of the strings would be altered and they would no longer be in tune.
Alternatively a string might "slip" on a tuning post, but the odds on this happening for two strings at the same time are very slim indeed. Again, I am just guessing that two strings went out of tune, could just be one.
Maybe somebody should ask GF.