Good info and great diagram, but it's not universally applicable.
Your setup shouldn't work as you've described it, but after looking at your diagram I can see why it's working for you... because
you don't have cable service, either TV or Internet; you have fiber Internet service. You don't even have a WAN signal on your cable lines, since the WAN connection is being delivered via Cat6 cable from the fiber ONT. Your setup, with the coax fed only from the gateway isn't any different than having used a standalone MoCA adapter at a router to provide the MoCA/Ethernet bridge for an isolated coax segment; the MoCA LAN signals are the only thing coming/going via the coax leg between the gateway and diplexer's "SAT" port.
A typical cable Internet service these days would conflict with OTA antenna on the same coax lines, both because the Internet signals will likely overlap with OTA signals but also because not subscribing to the associated cable TV service doesn't mean the TV signals aren't being broadcast by the cable provider.
An "antenna + MoCA LAN" setup equivalent to yours but subscribed to cable Internet service would require a dedicated coax line to the cable gateway and a standalone MoCA adapter feeding the diplexer (or a reconfiguration of the coax plant up-stream of a MoCA-capable gateway involving a "PoE" MoCA filter and additional 2-way split).