Pet support?

An interesting discussion came up in a neighborhood group.

Neighbor 1 recently adopted a female dog who had not yet been fixed, the dog was in heat and neighbor 1 left the dog in the backyard while they ran out to the grocery store.

Neighbor 2 owns a male dog who they chose not to neuter. The male dog breaks through a fence board and enters neighbor 1’s yard. The dogs then mate (confirmed by neighbor 1 who returns home catching the dog in the yard). The female dog ends up pregnant. Neighbor 1 insists neighbor 2 should support in vet bills/costs for the puppies. While neighbor 2 says they are not responsible. Thoughts on puppy support lol!?

***to make an interesting additional argument would it change anything for you if both dogs had gotten out of their yards, or it had been 2 cats allowed to roam free?***