Is cyclobut‐3‐ene‐1,2‐diide aromatic?

I think cyclobut‐3‐ene‐1,2‐diide is non-aromatic since there are two sp3 carbons (carrying negative charge), but my source says it is aromatic. Why?

Just because a carbon atom is negatively charged and has a lone pair, it need not be $$sp^3$$ hybridized. The lone pair could be on a $$\pi$$-bonding $$p$$ orbital with the atom hybridized $$sp^2$$. If you allow for this possibility, you find that the given ion can satisfy the $$4n+2$$ rule for aromaticity, which the text apparently is claiming.