Two characteristics isn't enough to define someone as a clone in any way. Especially when even having those two characteristics, they function differently. For example, let's look at their aerial capabilities.
Kirby fills himself up like a balloon and flaps his little arms to give him some air time with his now decreased weight.
King Dedede fills himself up with air as well, but he doesn't flap his arms. He holds them out and glides.
Let's also look at the other quality, Inhaling.
Kirby has a short ranged vacuum vortex and since he has no real stomach, it's a rather smooth process. As soon as they enter Kirby, they become a star that contains their qualities. Furthermore, Kirby can copy abilities using this.
King Dedede has actual lungs and more suction range. Though it's not really a magical effect like Kirby's, thus they are the same form inside King Dedede's stomach as they are when they are out of it. King Dedede also has much more might when reciprocating.
So the actual reality is the only thing remotely similar is the fact they can both pull in entites of nearly any mass into their mouths with a vacuum effect. Even then, it's just King Dedede trying to copy Kirby but not having his actual ability. No more of a copy then the fact both Meta Knight and Pit fly and carry swords.