1 {scene: darkness in the creepy castle in Transylvania}
1 SFX: Roo-Roo-Aroooo!!
2 Adam: Jamie, did you hear that?! A wolf!
3 Jamie: It was probably just the dog we met when we came into the castle.
4 Adam: You think the dog is a werewolf?! Whoa!

Searching the Internet for "can animals become werewolves" reveals a range of answers spanning the gamut from "yes, of course" to "no, of course not". Interestingly, both ends of the spectrum appear as answers to the same question asked on Quora, on Reddit's AskScienceFiction, on Reddit's Dungeons & Dragons Next, and on Reddit's Werewolves.

One answerer does point out the linguistic issue: that "were"/"wer" is actually Old English for "man", so "werewolf" literally means "man-wolf". So if a dog could become magically able to transform into a wolf, it should more pedantically be called a "hundwolf" rather than a "werewolf". But this just dodges the question of whether a dog can do that or not.