I'd say it it but I can see, why it isn't.
Our standard 3x3 is a cube, no questions asked. It has the same dimension in all axis and it's piece arrangements are 3 by 3 by 3. Certified as a cube.
Now, there exists a 3x3x9. Obviously a cuboid, not a cube - and I agree with that. But there is a fully Cubic 3x3x9. This is where things get a little trickier because the dimensions are all the same - cubic, but if you look at piece arrangements, it's 3 by 3 by 9, not cubic.
So move on to the Square-1.
Dimensionally, there is no current gen Squab that is fully cubic, the old Qiyi was only 1-2 mm away, would need a bigger equator, but one can see how it would be possible to design one.
This is where opinions come in. Look at a the top face, there are Corners and Edges if you draw two straight line around the perimeter, it's 3x3 pieces in line. Now flip to F, piece alignments are Corner-Equator-Corner and Edge-Equator-Edge, so always a three piece arrangement. 3x3x3 it's just that counting the Equator as an equivalent piece to an Edge or Corner looks like a stretch.
As for the cubeshape part, difficult. A mirror cube, which shapeshifts is for the most part considered a cube. But in contrast, Squab's CS shenanigans are a bit more extreme.