I was for many years (5ish?) a camp counselor at a all-boys summer camp (then, it's since become co-ed).
I promise, your son is not alone. Cannot begin to tell you how many times I was up at 3am helping out a kid disguise a wet sleeping bag. It happens, parents just don't talk about it in the open much - so everyone assumes there's something wrong with *their* kid.
Has he had a growth spurt recently? Or has this been sort of a on/off thing for years? Normally, bedwetting is a hormonal issue, where the body isn't making enough of a anti-diuretic hormone that's naturally secreted overnight (called ADH, or vasopressin).
If he wasn't making enough of said hormone though, he'd likely be having more regular frequent nighttime accidents.
Because it sounds like it's just once in a blue moon for him, I honestly wouldn't let it stress you too much. It's just something kids deal with from time to time!
I wouldn't bother with them everynight, as it would be a huge waste if he's mostly staying dry. But - have you considered asking him how he feels about wearing one of the nighttime pull-ups to bed, if he's in a situation where accidents would be a problem? (on a trip, sleepovers, etc.)
They're very discreet, and he could simply slip one on in private just before bed, and no one would be the wiser.
https://www.amazon.com/GoodNites-Bedtime-Bedwetting-Underwear-Packaging/dp/B00U0NRI0W?th=1