Exactly; I wouldn't be worried at all if you said, "Well, I think alien life exists, and here's why; I think they may have visited us, and here's the evidence," rather than being dogmatic and saying, "Aliens exist and they've visited us," absolute, without referral to evidence or logic. The difference between having an opinion that alien life exists, and having a delusion that alien life exists, is that the person with the delusion will not be using logic or evidence to come to his conclusions; or if he does, the logic will be broken and the evidence will be illogical.
Incidentally, even if they were absolutely sure that aliens existed, and didn't have a decent argument (for whatever value of "decent" that they were capable of; I wouldn't expect as much from a C student as from a professional philosopher, naturally), there is still the possibility of merely having schizotypal personality--the odd, eccentric, superstitious person who is nevertheless still in touch with reality and does not have any outright psychosis.