no, not schizophrenic delusions...
it's a sexual fetish, mainly in gay men.
Then, of course, there is the sex. Puppy play is often part of a larger sexual practice that crosses over with leather folk, furries and BDSM.
when I studied psychiatry, we were warned that often when we talked to our patients, their delusions would sound logical. So we were told to apply the "taxi driver" rule: If the average taxi driver would think the person was crazy, the person probably is crazy.
but now, we are supposed to be accepting of such things.
related item: UKTelegraph lamenting abnormal sex is now the norm.
I have a countercultural idea:
Instead of "having sex" with a person you barely know, how about "making love" by marrying and being faithful to a spouse...