Astringency is a bitter, mouth-puckering, dry taste caused by tannins. Tannins can be extracted from grain hulls in a few different ways, but the most notable way is boiling. For this reason, you want to avoid boiling your steeping grains at all costs, and when steeping, you should shoot to keep your your water between 150-170F, no higher.
Did you notice any such off-flavors? Its possible the sweetness from the pumpkin might have covered it somewhat...who knows.