Not an SBR. It's on a pistol buffer tube, and you can't attach a rifle stock to it. If it were on a standard rifle lower with a fixed or adjustable stock, then it would be an SBR and require paperwork.
Any stripped lower can be turned into a pistol lower, as long as it hasn't been built out as a rifle previously. As soon as you throw a rifle stock/buffer tube on it, it's a rifle forever.