It’s not our place to judge or speculate on the faith of others who profess to be Christians. There is no good reason to do so. That is between them and God. God knows his own and can’t be fooled or judge them wrongly. Rather, our focus should be on our own relationship with God; that is is alive and bearing good fruit, and that we are becoming more like him everyday.
It’s anyone’s place to judge regardless of the circumstances providing it doesn’t take the form of personal harassment. However, being considerate and possibly showing empathy is preferable when possible.
One’s relationship to God (or lack of) is certainly a personal matter and no doubt unique to each of us.