Here is what I take
@Remathilis's claim to be:
In AD&D (Gygax's PHB - I don't know how different 2nd ed is), both Gnomes and Half-Orcs have a minimum strength of 6.
In AD&D, a male Half-Orc has 4 times the chance of having percentile strength as a male Gnome (roll of 18 vs roll of 17 or 18, because of the +1). There is then a 50% chance of having a greater percentile roll.
So out of 206 Gnomes (ie rolls of 6+ on 3d6) compared to 212 Half-Orcs (rolls of 5+ on 3d6, as the +1 brings them to the minimum), 2 of the Half-Orcs are stronger than the strongest Gnome (ie of the 4 who rolled a 17 or 18, the two who also rolled 51+ on the percentile dice).
That does not suggest some wild difference in strength across the two populations as a whole.