A lot of the parts inside and out sure look like the M4.
The HK MR556 is not the same as the 416. It actually uses some AR15 parts where the HK416 does not. The HK416 uses quite a few more proprietary parts than the MR556. The MR556 is still very different from an AR15/M4.
And yes, Combat Diver is correct, however I do think that the piston system rifles are better if they are executed properly. Such as the FNH SCAR, CZ Bren, LWRC M6, HK 416, Galil ACE, etc... the Direct gas impingement system and the M4/M16 rifles are very very reliable and the difference between them and the piston guns in the real world are very small if you do it all right. The DI system is also far cheaper.
I'm still sticking with my LWRC piston system rifles but there is nothing broke on the standard gas system of the AR15. The lWRC shares some parts with the AR15 but is largely proprietary as well.
The LWRC "Individual Carbine" series was actually designed a few years back in a contest that was held to replace the M4/M16. And even though some contenders may have faired a little better than the M4/M16. It was not a huge difference and was definatley not worthh the significant increase in cost for the new rifle system designs.
If you want a Piston rifle, buy a piston rifle, but don't think that there is anything wrong with the DI rifle.