from https://www.fnha.ca/Documents/FNHA-Territory-Acknowledgements-Information-Booklet.pdf (i might be being too literal but thought it an interesting question)

No, it's something I've been wondering for a while; not to exempt Philly from the US's generally dishonorable history in this area, but there actually was a treaty and a purchase at the outset, which seems like it complicates things.