Pins 4 and 5 on each of the forward 9 pin sockets are the heaters for the tubes. Each tube's heater has pretty low resistance, and they are all in parallel, therefore pins 4 and 5 will look to be about shorted together, and pin 5 on each of those sockets is grounded.
If there was actually an issue, your voltages check would have failed.
For what it's worth, if we rewrote the Eros manual today, we would not have a resistance check for those pins.