If I understand you correctly, the pieces of the file you are downloading are also being shared by PFS ("Partial File Sharing"). The complete file hasn't been shared "600" times--just some chunks of it.

So--that likely means the original few sources of the file are very busy, but once one of the new rarer pieces is available in the download mesh, everyone gets to grab it.

You are sharing the pieces you got, others are sharing the pieces they got, and the original source(s) on their busy/slow connection are slowly offering the pieces no one else has.

Keep on sharing--sounds like you have a great connection and setup.