There is just no way that it is a 1978 laserdisc, the only things being produced then were the discovision discs, and they had only just barely started in production, PAL laserdiscs didn't even exist at that point - who would manufacture a PAL laserdisc for a market that simply did not exist in any form. There was no such thing as bootlegs until later in the Laserdisc lifespan - the real companies were having enough trouble producing discs that worked.
Basically no one in the general public even owned a player at that point.

My guess is that there is a copyright notice of 1978 on it - perhaps referring to the copyright date of the film print used in the transfer, but I will give you both my testicles if it is a PAL laserdisc manufactured in 1978 of ANH.