An AR-15 is not a heavy machine gun, and an MRAP is not a tank.
It’s relative to what you are going up against.
An AR-15 is a heavy machine gun if your opposition only has a shotgun.
An MRAP is a tank if your opposition only has a bicycle.
Drug dealers in Mexico make “tanks” to go up against other drug dealers. They don’t have the firepower to stop them so in their eyes it’s a tank.
It’s not a heavy machine gun or tank as defined by the military, but as defined by the people they are used against.
In a lot of cases it’s just a convenience of words.
Try taking on a MRAP with shotgun and tell me you wouldn’t call it a tank.