I saw in a video that a Villain donked 1.5x the pot OTR after xc Flop and xc Turn. 

GTO said we should call with 40% with all our hands that we have at this point THAT BEAT A BLUFF.

I understand the 40%. But not why we shouldnt call with 40% of our entire river range. Why only 40% of all those hands that beat a bluff. 

This makes our calling range very small, doesn' it?

Thanks again so much