Revenant's Spooky Aura!

[Houka]

ghosts have no physical presence and could not do either of those things

Ghost sprites are clickable. This is what allows you to point-blank them with the ghost gun. They also overlap players. If they are visible, they get in the way of the ability to click people or objects. It's more how interacting with things in this game works and not an issue of whether ghosts are tangible or not.