Just wondering, Im a non muslim and why im treated differently when i replied to their greetings
When i was greeted by iranians (or arabs) with this and i replied back waleikum-salam. There seem to be no problem
However, sometimes when i replied waleikum-salam, malays or malaysian muslims give me certain stares like WTF? U playing with that word?

Seriously, my question is it illegal to do so?

because i feel weird if i don reply back a greeting, i just greet them back with that. i guess its not wrong right?

actually seldom local muslims directly salam me face to face. mostly on phone.
but imagine a situation here. u're in a lecture hall then lecturer comes in and greet just that and not good morning or anything. just that word. of coz sometimes my mouth auto blurt out the word.