I'm not an expert on the laws of rugby, but surely something has just gone terribly wrong. The decision on whether to blow the final whistle should not be based on how long it takes the referee to get the technology to work, and to ask the other official whether time is up. The only question should be whether time was up at the moment the ball went dead, in which case the answer was no. And it's obvious that the Welsh players had the objective of winding the clock down with their actions after the Scotland try was scored, so surely the referee should have stopped the clock for a few seconds anyway?
OK, it's natural to feel a bit raw ten minutes after an incident like that, but this one really does seem like a clear-cut case of injustice.