No, because there’s no “understanding” of language going on here. The dogs are responding to a trained stimulus. I could train a dog to sit when told to stand and they wouldn’t be confused at all because it isn’t the word itself they’re interpreting and responding to.
ETA: Downvoters need to stop anthropomorphizing their animals. It’s not healthy for you or them.
Your dog understands the sound you make and your associated intention when you say “sit” in English because that’s what they’ve been exposed to the most. Do it enough times in Spanish and Japanese and they’ll eventually figure those out, too. That doesn’t mean the dog understands how to say “sit” in three different languages, it means they understand you’ve got three different “sounds” that mean you want them to sit.
Were these researchers under the impression that dogs actually understood English before the experiment?
That headline definitely took a second to parse.