This post was made by a character that has since been deleted.
Not a bug, as thumping was intentionally changed to work with vision range instead of hearing range a while back! This also would work if you had a limited vision for other reasons, darkness, poor vision, etc.
Fixed that Blind characters were able to notice Thumping at all. As mentioned by Faithil, Thumping isn't morse code and requires you to be able to see the person's movements to interpret what they're trying to say. They can still give messages in Thumping, but not receive them.