I could think of a couple of examples of how pawns can get into multiply tournaments.

1) They were a knight/rook whos membership has expired, but are still playing in other games.

2) During the "new year bug" when games were timed out, a pawn may have had their games gone, signed up for another tournament, and then got their old games back.

3) A known game bug which I have reported to Fencer at one time of how a pawn could enter multiply tournaments, which when I last checked was not "fixed" yet.