They are probably calling Grimcringe a pervert because in the image Grimcringe sent, Ellen's breasts are hanging down the image and it makes up approximately 15-20% of the image (don't worry, Ellen is fully dressed)
Grimcringe sent the image to prove that Ellen is freaky when she was seeing something and breathing through her mouth.
Reimu loves touhou so he would use touhou-related images so Penid, there is a chance you might be correct. Or he might be overreacting to Grimcringe's image or smth.