Thomas is their nickel corner. Giants have gone nickel most of the game twice now vs Philly. Last time Will Hill filled in for Thomas and had a big game. This time Mundy was banged up, so Hill was at safety, and Webster was banged up so McBride started at CB. Depending on the matchup, Thomas could have a good game again, but I think Antrel Rolle is the Giant DB you want.
Looking at their schedule, perhaps it's not a fluke:
vs OAK - do they have 3 WRs? - bench
vs GB - do they play anything other than 3 WRs? - start him
vs DAL - Austin back? - start him
at WAS - should be running the ball, but pass constantly when tied or down - tossup
at SD - passing team - start him
vs SEA - Harvin in but Rice out - not enough nickel usually - bench
at DET - constant 3 WR sets even though they keep losing WRs - start him
vs WAS - should be running the ball, but pass constantly when tied or down - tossup
This all precludes Mundy getting healthy and getting his safety job back, and Hill/Thomas not splitting nickel corner snaps going forward. In other words, it's not a given.