Crossed wires

I visited a friend today, and now I have a question.

I usually get along well with cats, but one of my friend's cats (she has two) has always been a bit cranky around strangers. The only time he even started to almost tolerate me was when I cat-sat for three days a long time ago, and even then it was only for about five minutes just before I left at the end of the three days. He'd recovered from his momentary lapse by the next time we met, and usually when I go to her house he hides under the furniture, and snarls and spits if I get too close. I've always understood that to this particular cat I am a highly suspicious character, possibly a door-to-door religious salesperson who should not be encouraged. He has never trusted me, and I have known him for at least half of his life. He is fourteen years old.

Today, however, when I turned up he treated me like a long-lost friend. He wrapped himself around my ankles and begged to be picked up, and when I did, he purred and cuddled into my shoulder. This made me feel all warm and fuzzy but was also somewhat disturbing. It was especially disturbing a bit later when I was stroking him, enjoying my new privileges, and when I stopped my friend took over, and he got all irritated and scratched her. He seems to have mixed us up.

So my question is this: How did the wires in his fuzzy little feline brain get crossed like that?

Do cats get Alzheimer's?