Hm... okay.
Considering the drama that occurred between 'Blue Mage' and 'Trickster', I think that if you ever 'borrow' a concept from someone else, or if someone recognizes that idea in any of the leveling systems, you should attribute them (even if they're not as active anymore), just in case they come back and see a part of their idea being in the Crucible.
Granted, if you had a whole new concept for the ability, 'Gluttony', the only thing between your idea and Schattenfresser's idea would be the name, which doesn't need that much credit (several card ideas on the board share similar ability names, but have
totally different mechanics).
So in all - just add his name in the 'IDEA' section of the table, and it should be good. Giving credit where due is always nice.