Ground rule double is correct.

They argued that since the ball landed foul, it was a foul. It ended up being a moot point, however, as the batter ended up on base anyway and scored on another batter's 3-run home run.

part of the field’s ground rules. Never should have been an issue once the game began.

Mike Schmidt hit speaker in Astrodome turned a monster home run into single

Kingman hit one into the roof if Metrodome was ground rule double.

Apparently, it's suppose to be discussed pregame.

Seems like easy to make a universal rule but baseball baseball i guess

If the batter was from the visitors team home run, if from the home team foul ball. The dome was an impediment caused by the home team. Just stirring the pot.

Since the beginnings of baseball in the 19th century, players have adopted unwritten rules about how to behave during the game. According to sportswriter Ross Bernstein, these rules have evolved over time. Joe Garagiola wrote a book about baseball published in 1960, titled Baseball is a Funny Game, in which he mentioned the unwritten rules of baseball.

"Baseball is a game played with bat and ball and governed by rules set forth by a committee under the direction of the commissioner of baseball. Baseball is a game played by human beings and governed by unwritten laws of survival and self-preservation.
— Joe Garagiola"

Wikipedia