Interesting! I always thought the tape releases were mono for some reason. Alas, my betamax is in storage with all my other gear for the foreseeable future.

Tapes were sometimes mislabled in the early days of Hi-Fi, or not all the duplication facilities had upgraded their equipment. (Hi-Fi could actually be switched off on some industrial recorders.) I even had an LD of an unrelated film with no digital tracks even though the jacket had digital sound markings. A second copy I later found of similar vintage had digital sound as advertised.

The LDDB has a PAL copy for sale, but the tech specs say that release was mono.
https://www.lddb.com/laserdisc/39163/LVG-1015/Buck-Rogers-in-the-25th-Century