Why do some muslims pray believe in christian saints?

When i used to go to annaya mar charbel i used to see muslims praying and kneeling in the monastery. I always thought it was weird and confusing but it could make sense as mar charbel is a very active saint and does miracles with a lot of muslims.

But ive seen countless other muslims in random churches and chapels praying.

Can anyone explain how a muslim can believe and pray to a Christian saint if the saint followed christ to become one. What are saints considered in islam? Because i know that praying to anyone that isnt god is a sin.