This is actually a rather interesting question because there’s a bit of debate about it. You see, taxonomically and up until recently, poochyena were considered a canine pokémon. Many researchers still classify them as such when describing their behavior, as they behave very much like true canine pokémon (forming packs, hunting as a group, guarding territory as canines would, and so forth). In this regard, they’re often though to be the Hoennian cousins of growlithe or houndour—the latter especially, given the fact that poochyena’s behavior most closely mirrors that (possibly owing to their shared dark type).
However, genetically, it was recently discovered that poochyena are more accurately their own classification and that this branch of the pokémon evolutionary tree is less related to true canines and more related to … zangoose. Both families belong to, of all things, the feline class of pokémon; it’s just that they adapted to fill completely different niches. While zangoose is technically more cat-like than poochyena (albeit, yes, zangoose is still not a true cat, and in any case, skitty fills that ecological niche for Hoenn), the going theory is that poochyena developed canine characteristics due to the lack of a true canine species in the region (vulpix notwithstanding, as it only lives on a specific island on an island).