He is referring to the 2x crop factor over FF.
I've shot a lot of video with M4/3 cameras GH2,GH3,GH4 but have moved to a pro body camcorder (Sony FS7) and am thinking of posting my M4/3 glass and GH4 body on kijiji and buy an A7s to share glass with my FS7.
My fav portrait lens for the GH4 is Pana/Leica 42.5mm f1.2. Great portrait lens (85mm equiv) and the IS is so handy in a portrait lens especially for video. The best part of the M4/3 mount is how many different brands of glass can be adapter to it (AF is crap with adapters or non existent but I shoot mostly video). I have Nikon, Canon, Panasonic, Olympus, OM, Pentax and some great funky russian M42 lenses all adapted. So many cheap vintage glass options full of character.
M4/3 shines over full frame for size. A GH/EM body with a 12-35 & 35-100 will fit in a very very small bag where a FF 5D/D810 with equivalent glass would take up an entire backpack. You can get close to portrait DOF on M4/3 but will never get the same look a FF sensor gives. For video in M4/3 a metabone speedbooster adapter is essential to get to my fav sensor size for video S35.
here is my production company site
www.framefarmmedia.com