Actual Heigt and Width of an MKV video

I have MKV video files that, from the site I got them from are supposed to be 704x480.
However, when I put them in MKVmerge or check their properties in Media Player Classic I find this-

Video: MPEG4 Video (H264) 704x480 ***(853:480)*** 23.98fps [Japanese, Mnemosyne - 01 (DVD) (Video 1)]

the italic-ed part is what the actual video resolution is when I play it on MPC. I checked with another video I had that was 704x480 in size then played the MKV video and the player got bigger.
In this case, how do I know the ACTUAL video resolution? Is it the one stated by the site or the bolded part above?