Well they can still get erect, and neutered male cats have been know to umm, masturbate with sheets, stuffed toys, couches etc...so I would say yes.
From some quick googling it sounds like the 'fluid' might reduce in quantity as he ages.
How much fluid did you find? I wouldn't think even an intact cat would produce very much. Are you sure it wasn't drool or spit or something??
Here's one from http://www.vetinfo4cats.com/cmale.html#Masturbation
|Q: I have a 5 year old neutered domestic longhair and he has recently taken to acting sexual with the blankets in the house. I had him neutered at 6 months of age, so I can't understand why this behavior would be popping up. No pun intended. He can get rather annoyed when we try to interrupt him, but when observed it must be stopped. I have on occasion turned him over to inspect his penis and just as expected it is erect and there is some discharge. I would love to hear your thoughts on this problem. Sincerely, Kandy
A: Kandy- Masturbation is a difficult problem to deal with in cats. It is a normal behavior and it is probably pleasurable. This combination makes it hard to discourage. It is not really unusual for neutered cats to learn to masturbate and it may be possible for them to produce some fluid.
In a few cats, this can become (or possibly starts out as) an obsessive/compulsive disorder. If this is a really persistent problem rather than an occasional one, it would be a good idea to ask your vet if there is a behaviorist in your area who you can work with to help resolve the problem. In this case medications for obsessive/compulsive disorders may be helpful. As far as I know, these are the only cats in which medication is likely to help.
I wish I had some sort of easy advise to follow for this problem, but I don't.
Mike Richards, DVM