Personally I would say the latter, but historically the UHECR community has been prone to say things like the former. (E.g., when AGASA failed to detect the GZK cutoff, everyone was like “there must be new physics allowing particles to evade the cutoff!”, as opposed to “there must be something wrong with the experiment” -- but given that all later experiments have seen a cutoff, it's most likely that AGASA did indeed do something wrong. OTOH I can't recall anyone making “planetarium”-like hypotheses, except jokingly (I suppose).)

EDIT: Also, I can't count the times people have claimed to detect an anisotropy in the UHECR arrival direction distribution and then retracted them after more statistics was available. Which doesn't surprise me, given the badly unBayesian ad-hockeries (to borrow E.T. Jaynes' term) they use to test them. And now, I'll tap out for, ahem, decision-theoretical reasons.