How about this: the designer took a basic tube preamp circuit and "converted" it to op amps, part by part. SO it has the same basic configuration as a couple of triode stages. So in that sense, I bet it really is a grid stopper.
"The resistor is an RF "stopper", and helps prevent RF pickup and demodulation. The general scheme is described in the amp design article.
But effective or not, efficient or not, we now do know WHY it was there.
In the TUBE world, the input resistor 47k to the GRID and 1Meg to ground was a low pass ckt to get rid of RADIO interference. This also is used for FET Opamp’s circuits.