You mean the vapor chamber can crack and release that vapor?
Potentially yeah, same as heatpipe, but heatpipe is very unprobably because it's cylinder, this is basicaly square, so the pressure inside on the edges are far bigger. Let put it this way, you know those pressure cookers? Well if you heat it to big temperature, it starts to, by design, release the vapor from the chamber.
However vapor chamber is plane, not cilinder and it does not have this valve, so shit can happend and the vapors could be just by different pressure inside. We don't know, I think it's more likely that cap on PSU, however we are not going to find out till someone tear it down and see the damage : )