How old is the kitten? Spayed/nuetered cats retain the ability to manufacture a certain amount of sex hormones, so they still may get an occasional "urge", they just "shoot blanks". I have personally never seen this in a spay, but it may happen that they also have some sexual tendencies remaining. Also, if the kitten is of the age that he is possibly transitioning into adulthood, Tsoomi may pick up on the female hormones that would be surging. All mammals make male and female hormones, and they both surge at puberty, and Tsoomi may be able to sense it.

That all being said, homosexuality does occur in the animal world. We had a dog we were sure was gay. My dad refused to let him be neutered (like a dog is really aware of his b#$!s) and we never once saw him mount a female dog - he only went for the males! Got really embarrasing!