Yes, it is a fursuit. Yes, "costuming as a human-sized cat" is fursuiting. Yes, the creator (Mikeneko Yamada) is a fursuit maker specializing in cat suits, but has also made a tanuki, a bear, a shiba inu, a frog, and several more that I've seen. Yes, the fursuit is both hyper-realistic and anthro (it's on two-legs, thus exhibiting human-like behavior and that's all anthropomorphic really means). No, fursuits don't have to be cartoony sparkledogs to be fursuits. Hyper-realistic fursuits (like this) and quadsuits exist. They are still fursuits. Yamada, the creator of this fursuit, blogs their exact process making fursuits with the EXACT same processes other fursuit makers use to make fursuits, down to the jawsets and head rigs and air fans absent from many non-furry mascot costume work. This is a fursuit.
Idk why people feel the need to distance themselves from liking furry. It's such a wide genre. It's not all Disney's Robin Hood, Beatrix Potter's art is furry art too! People like to try and compartmentalize it into the tropes that make them cringe but for everyone out there participating in furry fandom some way you don't personally like, there's another person out there doing something like this you think is cute or fun or interesting. It's diverse, and people on the internet need to stop acting like they're allergic to furries every time they see a furry do something they actually like.