To be fair, it's a relatively low risk play, they're on megas, their carries are alive, half the enemy team is dead so they probably won't be pushing for a while and he might have buyback(not sure). Buying a rapier with no buyback/aegis on Luna when you've been dying first on every teamfights for the past 10mins is quite a bit more ballsy.
Also they probably would have won a lot earlier if they had been able to keep the gem on someone alive to deal with S4. How many teamfights they ended up losing/drawing because S4 was burrowed and spamming stuns the entire fight because Puck would die instantly from mana burn+some other random shit and then they'd have no vision.
Still by far the best game in the tournament I think, and best game in a while. After the first 2 games it's even more surprising considering they were losing at first and still didn't give up.