If that species is managing to survive - and thrive, considering they've lasted long enough to get to the interstellar travel stage of societal advancement - on its own planet, it wouldn't need to travel through several solar systems just to find something new to snack on.
If suddenly, all the livestock on Earth died due to, let's say...hell, I don't know, some really terribly bad disease that for some reason only wipes out cows, chickens, pigs, etc. (don't think too hard about it, it's just a hypothetical disaster scenario), which do you think is more likely - that we'd look for another source of meat (humans are omnivores - we can survive without meat, as the vegans have proven, but it takes a very carefully balanced diet [which I have no intention of trying, on account of how I fuckin' looove chicken]) within our own planet ("Elephant steaks, anyone?"), or that we'd take pains to build a massively advanced space ship to go trawl through space, on the slim hope that there's a big, yummy animal that tastes like porkchops wandering around on a planet somewhere? And even then, we'd have to hope we'd even be able to digest it, or that it'd nourish us at all.
We are omnivores, so we eat both meat and plants, and we are capable of sustaining ourselves without meat (but, as I have said, chicken is delicious, so fuck that). Now, let's suppose the aliens are carnivores. They only eat meat, and as humanity has proven, breeding your own meat in the form of domesticated livestock is a lot easier than going out with a bow and arrow every day to shoot a rabbit (although which is more fun...that's your own opinion). They'd know the chances of finding a species out there that they'd be able to sustain on their planet (also super unlikely) and that would nourish them in the ways they need are slim to none. They'd begin by looking for an answer within their own planet.
Or they'd die out. That's also plausible.
What if dorfs ARE ALIENS? Like they were here in the past and have since atomsmashed all the world's dragons and elves, and then they took off in magma powered saucers?
...
Sorry, I'm trying to think of an expletive that properly reflects how much I hate you. I'll be a while.