Second Pressure releif valve in hot water system?
I have not heard of a TPR valve being required outside or further away from the water heater there would be less of a chance of valve opening for temperature the further away it was from the heater. I have seen reliefs on hydronic systems at a lower pressure to protect the embedded plumbing but not water heaters. Possibly a work around for a drain that the one at the water heater did not have.