Does anybody know what the data source for this is?
No network traffic is generated after the initial load so my guess is that this JSON file is generated on the server from some other data source and is read on load and then continues to calculate positions from that initial load. The data on the server changes every 10 - 15 minutes it seems...must be a script updating it.
Some of the API names from space-track match what's in TLE.json, so it's probably just fetched and post-processed every couple minutes.