The blog speculates this was for space-saving reasons, meaning the mute switch (which can also be a rotation lock) was sacrificed in order for Apple to attain the desired thinness. Video below.
It isn’t clear what stage of development this ‘iPad Air 2′ is from. From the pictures, it doesn’t seem like a mere dummy unit, but the poor finish on the back side appears to suggest this is somewhat of a prototype and not ‘final’ hardware. However, the video almost certainly depicts a dummy unit, which may offer an alternative explanation for the lack of mute switch (simply incomplete dummy).
Bloomberg has previously reported that the new iPad will feature an anti-reflective screen. The Vietnamese blog could not turn the device on, so this claim from the rumor mill could not be corroborated. It is also expected that Apple will release a version of the new iPad Air in gold.
Apple will announce the new iPad by the end of the year. More specifically, it is highly likely to be announced at an event on October 16th alongside Yosemite release and new Retina iMacs.