At one point in time, (I think maybe in connection with some mobile phone being able to play .midi files?) MIDI songs was (incorrectly) referring to a style/type of music rather than the transport/protocol we use for sending notes between instruments/devices, or the file format.

I'm still since then always assuming the above when someone says "MIDI music"; they really mean "really basic/simple music" or just straight up "chiptune" sometimes.

It has nothing to do with MIDI really, just a misnomer.