I think you misunderstood the ruling.
Exactly how did the poster misunderstand the ruling?
It’s the court that misunderstood. The court said that the amendment violated the First Amendment (no establishment of religion) because it delcared that Islamic (religious) law violated American law, which the court assumed to be based on Judeo-Christian law.
The problem is that Islam is a theocracy, and therefore Islamic religious and civil law are one and the same. Christianity is not a theocratic system; at times churches (think of Calvin) have tried to impose their canon law as secular law, at times churches have been dragged into this by the lack of secular law in a given place, but essentially Christianity does not dictate civil law. Islam does.
So the court is essentially saying there is no recourse against Islam because it claims to be a religion. This was one of the Devil’s greatest gifts to Mad Mohammed: Satan told him to cloak his project of conquest in religion, which Satan knew, back in the 7th century as now, would protect it from scrutiny.