Regularity condition of 3rd Case of Master Theorem. Need explanation

Question

I do not understand how regularity expression was constructed in Wiki example for 3rd Case Master Theorem. Here is what given in Wiki

Shouldn't it be $$2(\frac{n^2}{2}) \leq kn^2$$ for regularity condition?

If we have b = 2, how did we get 4 as our denominator?