On what’s app can people you have not added as friends send you messages?

[jennifer_bloom]

I received a message today from an unknown profile and I think it’s my African enemy pretending to be a Chinese guy because he wants to trick me into giving out my personal information so he can hurt me. I know every person who has my WhatsApp cause I don’t give my number to just anyone so I am pretty sure someone on my list is using a fake identity to bait me and he is the only enemy I know who has access to my phone number.

[The_Shadow_Dweller]

Yes.
WhatsApp works completely differently as compared to Facebook.

On WhatsApp, you only need to have the number saved. Suppose the person who's number is saved in your phone, does not have your number. Then, when you message them, the software asks to keep the chat or block it or report it, to that person.

Same thing can happen with you. Someone can have your number and decides to message you. Yup, you get the message.

But regarding the profile picture, if the numbers in a chat are saved on both the ends, then the profile pictures and the names are visible, otherwise they're not.

[Massageman]

a blind box in Hotmail.

[RedBullRacingLemia]

They must have your number to able to message you.