I was just coming to say the same thing
@IceIce9 said about the PBT/Breathalyzer testing. But I do want to add that there are meds that can show up as a false positive in a narcotic blood/urine test. HOWEVER remember that this was a 7 day cruise. Meaning that if these were prescription drugs he would have had them with him, and would have easily been able to provide the information of what drugs at what dosages he takes so they could be taken into consideration.
This wouldn't be handled like a drug test at work where it's "oh! look! it's positive you're on meth!" A clinical toxicologist is perfectly capable to get back a toxicology screening and compare the results to see if the metabolites found would be at the same therapeutic levels that you would normally see for the dosages of the meds he's taking and be able to say "Oh yeah, that's clearly his antidepressant/pain med/whatever."
I am curious though. Here's a list of some meds that can (not always) give a false positive. I'm sure we have members who take these as they are some pretty common drugs. Were any of you guys aware your meds might give a false positive? The link lies there's 20 on the list not 15 lol.
20 Medications That Can Cause a False Positive on Drug Tests - GoodRx