That certainly seems to be the implication. The poem talks about Grendel having "forsworen hæfde ecga gehwylcre.", literally being impenetrable to (foreswearing) bladed weapons due to the "on féonda geweald", the administration (work) of fiends (demons).
Taken at face value, the writer is saying that Grendel can't be harmed by a bladed weapon because he's been cursed by demons.
The protector of earls had no wish for any reason
the murderous guest to release alive,
nor his life-days to any people
counted as advantage. There many brandished
warriors of Beowulf, old heirlooms.
they wished prince-lord's life defend,
the legendary leader's, if they could do so:
they did not know that, when they joined the fray,
the bold-minded battle-men.
and on each side thought to hew,
to seal: the soul: that the sin-scather
any on earth. of the choicest of irons.
of war-bills. none could not at all greet him
but he victory - weapons had forsworn.
every blade-edge. His life-severing was bound to
on that day in this life
be wretched. and the alien-spirit
into the administration of fiends would journey far away: then he found, he who before many, miseries in his mind. on mankind atrocities committed
Obviously this doesn't prevent our hero from ripping Grendel's arm off and trying to beat him to death with the wet end.