ok! I think that's a logical flaw, solipsism is a floor.
"I can't be certain about anyone else" does not imply "all non-self consciousness claims are equally uncertain". absence of certainty and the absence of evidence and all that.
your "possibility" word is doing a lot of work there I think. you should add "rocks" to your list as well and you'd be equally correct, but we're evaluating the candidates here