CSN-Philadelphia is a weird channel. It's not broadcast via satellite; it's still sent via wire. DirecTV does not carry it.
If CSN-Philadelphia is not available through the poster's cable system, s/he will be allowed access to it via Center Ice. And, if s/he has DirecTV, since the channel is unavailable, it cannot be blacked out through Center Ice. CSN-Philly's signal is re-transmitted and compressed to get to satellite.
I'm guessing s/he lives somewhere in Northern Middlesex, Somerset County, or near the beach in Monmouth. Most likely NHL.tv considers the area "Philadelphia" because Philly locals are probably available on cable, or OTA.
A similar situation occurs in upstate New York. The region is considered Sabres territory, although the RSN is MSG. Therefore, the Rangers, Devils, and Islanders are considered local teams too. On cable. there's only so much bandwidth that most times the Rangers, Devils, and Islanders are bumped. The only way to see the games is through Center Ice, or via DirecTV, which does not have the bandwidth problem.