I'm not that person, but presumably it's that someone has purchased real estate in a geographically relevant location and constructed property on it/between it

I'm not that person, but presumably it's that someone has purchased real estate in a geographically relevant location and constructed property on it/between it and the exchange which gives them an insurmountable latency advantage in HFT, and they are characterising the raking in of cash from that latency advantage as rent seeking.