I think he feeds the birds safflower seeds. Squirrels don't eat 'em, which is why my post feeder is exclusively for safflower seeds. LSA
Didn't ask him about the gray birds, though....had muh mouth full of stuff at the time.
Another effective squirrel deterrent (other than gunfire) is a cayenne-pepper powder that is mixed into the seed. Birds can't smell or taste it, but squirrels can. And so can I. Nasty stuff.
I put a hugh pile of seed treated with this stuff on the ground for the squirrels. The first squirrel took one whiff, and jumped backwards about three feet. The squirrels backed away from the seed as if it was radioactive, but the birds skarfed it down as usual.