Zoning laws vary city to city, state to state, so reality may not conform to what the City says is there.
But I agree with Dublin Ohio: if access only through main LQ, then its not an ADU per se, and just additional living space to the main house. Was it a build? Permitted addition? Hmmm... If it has an outside entrance but still attached with possible access from main house, you may call it an ADU, or additional GLA if permitted (or mini-ADU). The fact remains that the square footage is there, and you have to call it something. If only SFR zoning on that lot, and square footage is permitted, I'd lean to SFR and include all the GLA. If you call it an ADU, or a "granny flat" (uh oh, my Fair Housing module says that's a discriminatory word), then you will likely need a comp with the same situation. Good luck with that.
In CA, I'm finding more than I expected, houses have "secret" rental areas. Saw one today. The first floor 2 bedrooms & bath had an exterior door put in, and the previous owner rented that space out. Current owner used the whole house and took off the door in the hallway that separated the LR from that BR/Ba wing. And even if not actually 'legal' to have an ADU, some ppl will put in an outside door, install that pass-thru door and say their "roommate" occupies that space... all perfectly legal up to a point.
So you probably could call that space several things legitimately. And the "kitchenette" in there? 'Oh yeah, that's where we store our snacks when we watch TV in our 'gameroom' here'. Duh.