Rules 28.731 states: The victim must remove all tokens from two of his areas sharing a common land border. Both areas must contain at least one token and must not contain a city. The victim chooses which two areas will be depopulated"
The Quick Chart states: "Victim must select two adjacent areas which he controls and remove all, max five, tokens from these areas".

Does "common land border" mean "same land border with another player"?

Or does "common land border" mean "two adjacent areas that are connected by land"?

The Quick Chart Ruling would imply that a maximum of 5 unit tokens are removed from 2 adjacent areas not containing cities, connected by land, anywhere in the players empire. Is this interpretation correct?

What reasoning are you following when you involve another player in the rules, when the rules only states that a land border must be common between two areas (eg a land border that is a land border for both areas, eg the two areas are adjacent).

Other parts of the rules does speak of a land border that is common between two players (eg a land border that is a land border for both players), but as 28.731 doesn't mention another player, there is no way to infer "common to two players", when the rules explicitly says "areas sharing a common land border".