Actually, non sequitur is a fairly common term. I wouldn't assume that finding it used as a name at different sites necessarily implies the same person at all.
But then, maybe it's not a common term to birthers.
Also, if I were so inclined how long to you think it would take me to have “danamco” registered on DU with posts? The fact that there may be a “Non-Sequitur” signed up on DU is meaningless.