why do some people see ghost while others see saintly apparitions?

We read the energy out there and it has to go through our brain for interpretation. Some feel it in their bones, etc. Visuals have to pass through the part that makes pictures, like imagination, and while doing this the conscious mind has to interpretate what to make of this energy picture. So it depends on your beliefs. A religious person will associate the image to a saint, while a psychic or non religious person will see the image and probably take it a step further and try to "read" or find out who this person is. Everything is about information interpretation.

Its just a matter of interpretation to fit beleifs. I mean for example some christians dont believe in ghosts at all, only demons so if they see a ghost they wil call it a demon or angel.

There all the same the "saintly" is a ploy to gain people's trust. Never trust a ghost/ spirit. The only good spirit is GOD (Holy Spirit).