The magmeter needs the piping grounded for the sensor to operate. The mags I install have an internal reference ground, these mags are 24 VDC. I had 4 24" mags that had reference rings with a bond to a lug on the bottom of the mag transmitter. The mag body has an EGC with the supply circuit and that eventually is tied to the GE system
What I would do is to get the installaion instructions from the mfg and review the grounding details, and get the instrument submittals to see how the instrument was spec'd, if there is an internal grounding you are all set.
Often the plans (like yours) have some sort of generic details.