Can you get diagnosed with ADHD even if you don't have it?

I have been married over a year and recently learned that my husband was diagnosed with ADHD in college. Now he denies that he has it, and claims that he cheated on the test to get diagnosed that way on purpose. According to him, he failed in college and got kicked out due to his incompetence with writing (he tends to rewrite over and over due to his obsession to write perfect sentences, thus takes much longer time to finish things) and one of the professors suggested to him to use ADHD as an excuse to get back to school. So he "intentionally" got diagnosed with ADHD and back then took medicine, saw counselor, and showed some improvement, and thus successfully got back in and finished school.

He still has big issues with writing at his work, which he claims is due to OCD, not ADHD. The thing is that I suspected that he had ADHD from independently talking to my counselor about our marital problems, NOT KNOWING that he was previously diagnosed with ADHD. I could totally relate his behaviors to the ADHD symptoms -- forget things, unorganized, no patience, hyper-focus, anger outburst, selfishness, no empathy for me, hard to please, Jekyll in public and Hyde at home. His symptoms are milder than other people that I see on this forum, but I CLEARLY see every component on the list in him. And I have been living miserably from the Day 1 of my marriage because of his eccentric behaviors and thinking process!!!

What a COINCIDENCE that I noticed his ADHD behaviors with no prior information when he was diagnosed with ADHD only because he FAKED it?? Can anyone believe this?

Now all he cares about is to prove to me that he does not have ADHD (even though he is taking Adderall simply because "it helps him to process information faster" as he says). He says that his Psychologist does not think that he has ADHD. How shall I interpret this?  How objective is the ADHD test anyway? How can I really believe what he says when I see symptoms telling me otherwise?