A founder only has to be there for the beginning. "Early employee" and "left relatively quickly" would not disqualify him.
I know little about Sanger but he wouldn't be the first person to have been written out. Elon Musk's partner in early PayPal suffered that fate.
I think the thing is a soar subject because Wikipedia essentially rejected all of Sangar's ideas, but he's still kind of riding on its coattails.