The misunderstanding that many have about "crew-served" weapons is that the term is really a military one denoting that more than one person is assigned to the weapon.
It does not mean that it takes more than one to carry and operate it. Typically, the extra assigned body carries extra ammo and/or some other accessories.
I think some people use the term "crew served" to denote weapons that take more than one person to transport or operate or are usually mounted on a vehicle. The 249, 240, and 60 are not "crew served" in this sense but the M2 would certainly be.