It not true because apparantly the sex was consensual. That pumpkin was asking for it, with its come hither stem.

I heard that the real disturbing part was that it was anal sex....

And then there's the urban legend about the fellow who was brought into the emergency room to have a gerbil removed from his rectum.

Here's a list of other such, uh, items... including a "bottle of Mrs. Butterworth's syrup, an ax handle, a nine-inch zucchini..."

More straight dope on gerbil stuffing

how can someone sexually assult a pumpkin?