i keep getting a msg with only the outline of a folder, what could be wrong

[AC Question]

I have a cheap AT&T android which gives me unlimited text & 250 calling min a month for $28.00, this suits me just fine I don't need anything more expensive, but I keep getting a msg from a friend who has a flip phone, i have no idea what kind but he keeps sending me a msg (about 20 so far) and all they contain is the outline of a folder, no msg, just who it is from, no more. Since his phone is junk (lol) could it be he is unable to send text messages.
I really don't know that much about these fancy phone like I said I am happy with what I got. It's an AT&T Huawei fusion Y536A1.
I sure hope someone can answer this because it is getting annoying.

 

[B. Diddy]

Welcome to Android Central! Have you asked your friend what he's sending you? If he's sending you a photo via MMS, and your phone's mobile data is turned off, it might look like that.