THe M3 is an MSI board, there is no ASUS H170 gaming M3. The H170 Pro Gaming is ASUS and the H170 Gaming M3 is MSI.
As for what makes the Asus Gaming, its a lot of things that are a little more gimmicky than the real deal. The audio features are generally better and optimized for gaming and it has this sonic radar feature that supposedly can tell you the position of in game sounds (so you now where your opponents are), the networking is supposedly optimized to be low latency for better gaming as well. It has a better VRM setup for more stable voltage from your processor when its driven hard (TBH generally you only need these for overclocking which you can't even do with this board).
The MSI has similar types of features. Generally gaming boards are more "heavy duty" and can deal with excess heat better, with the thinking being that the processor is running close to 100% more often than on a regular everyday system.