That's the membrane from the inside of the shell stuck to it.... I usually yank it off if it doesn't come off with the shell... But honestly in usually wrong and pinworm is usually right so go with what he says lol
the humidity was too low thats why the seed got stuck. I would mist it a time or two with plain water that will moisten up the seed membrane up so it will fall off easier, just dont over do it and cause damping off.