It’s not whether the explanation is at all possible, but whether it is the most reasonable or most likely explanation. “Maybe bad fuel” is not “we investigated and found it was likely bad fuel”, it was just a guy spitballing, or repeating someone else’s random thought.

Trump is not known for making credible statements of any kind, let alone for being regularly correct in early appraisals of complex technical/mechanical situations.

So, could it be “bad fuel?” Sure, why not, I don’t know anything about military aviation troubleshooting. But is Trump posing the possibility a satisfying explanation? Not in the least.