Moto G / AT&T Help

Trying to help an older friend with getting oriented on his first smart phone. For some reason I've never encountered before, when he receives a text with an image (MMS Message) he only receives the text and a download link. Clicking the link takes him to some AT&T "mailbox" site (for lack of a better term) where he has the option to download the image. I've checked all the text settings & all appear correct & normal as well as, tried both the default app and, Google Messenger app. Why is he not getting his images to appear in his text? I don't know exactly what plan he's on but I do know it's on the lower end...could this be in play?, seems odd if it does.

Edited to add: After pondering on this a while, I'm betting his data is turned off. If so, he could still send & receive SMS but not MMS - however, since he was on my WiFi, he could download the attached photos. If it's not this, I'm stumped. I'm sympathetic to the guy, AT&T store pretty well just activated the phone & sent him on his way without any instructions other than how to turn on & off & answer a call.