This is, I am sure, a dumb question, but I read this https://en.wikipedia.org/wiki/XENON and I just don't know enough to completely understand the concept, but my dumb question is how do they know the event they saw was a spontaneous decay and not caused by a WIMP or whatever Dark Matter is? If it is such a rare event, how do we know that it wasn't a dark matter particle that caused it but the reaction was different than anticipated ? Can anyone take on a ELI5 here ?