It’s an AC-3 encode of the same track. It’s a DTS-HD MA encode in the MKV. Same with the 5.1 mix.
It should also be noted that while two “1985 Home Video Mix” files are included in the Alternate Audio folder, they’re actually the same as the 1983 theatrical mix, of which Schorman says the one marked “1983 - Stereo (US Source)” is the best quality.