You're right. The prosecutor would have had to prove the animal didn't enjoy the sex to get a conviction previously.
I speculate that law came about because of the persecuted Mormon sheep herders that was a large part of the original settlers or it could have been an Indian practice, either way the legislature changed the law last year.
And how do they know that the puppy didn't give his consent.
And it is after all NJ.
Where the men are men and the puppys are nervious.