Something didn't seem to ring true here. Off hand I didn't think Xenia had any Palytoxin in it. This seems to be confirmed by an article in reefs.com. You can read the article here -
https://reefs.com/2018/04/06/xenia-does-not-contain-palytoxin/
I suspect either the reef keeper misidentified the coral and actually had some Palythoa anemones in there or maybe it was something else in the tank they came in contact with.
There are quite a few things we keep that can "get us". It's never a bad idea to research anything you intend to buy. With most reef keepers having smart phones today, and net access almost anyplace, there is really no excuse.