Him hitting you out of nowhere with a passive aggressive "are you vegan?" was not the move, but you have to recognize a bigger picture here.
When animal abuse happens, and people see it, they are disgusted by it. It makes you feel awful inside, it makes you empathize with the animal.
But when animal abuse happens and you don't see it, people don't seem to care. I mean, what this fellow did to his dog is absolutely atrocious, but frankly it's mild compared to the 25 million chickens killed daily (USA alone), who are often hung upside down in assembly lines for hours, not to mention the atrocious living conditions they had beforehand. And that's just the surface.
Rather than passive-aggressively questioning your ethics like the other user here, I instead urge you to explore these feelings you have about animal cruelty, and think about what happens even when you don't see it.
On being able to comprehend, there are human conditions that are beyond my comprehension. I mean as an intellectual thought process I am aware why some people do certain things but it is so far outside of my experience that I could never truly comprehend why.
It doesn't have to, but in the case of eating animals it does equal cruelty. For what other pleasure than taste would there be this much bickering when the price is an animals life?
Let's stay with the dog in the picture, would it be cruel to stun it with a bolt gun, hang it upside down and slit it's throat? Not out of neccesity but because you like the taste?
IMO, not being able to comprehend cruelty makes someone an ass. The dude in this story could have been kind, polite... they could have helped mow the lawn of their elderly neighbor that's no longer able to do so themselves.
Regardless of how otherwise good you are treating a pet that you've accepted responsibility for and who, potentially, fully trusts you as family like this... that makes you an ass.
Anyways I think my only real objection to your original statement is that I don't think veganism is relevant to this story. I'd say that vegans are more likely to treat their pet well but it's not a guarantee - even among vegans that made that choice for an ethical reason there are still assholes.
Vegans might be nicer to animals but in my experience they're generally trash to other people. Also a vegan owning a pet is hypocrisy in the finest form.
Eh... they often are abrasive but it's because most of them genuinely believe that consumption of meat is unethical. I certainly don't appreciate being on the receiving end of their criticism but I can respect that it's at least logically consistent.
In general, though, vegans are against using animals for their matter and animal mistreatment. Ethical omnivores often refuse to eat animal products from factory farms due to the excessive cruelty involved in that process and vegans do take it further (I've always been a bit weirded out by their refusal to eat non-meat products like cheeses and the like but I do understand the logic).
Inviting a pet into your life, if you provide a loving home for them to be in, isn't against mainline veganism - though people keeping pets they can't properly care for usually is. It's all about making sure animals are treated well.
Some vegans just get hyper violent about it though.