Whoever they were, Amish, Hassidic Jews, Muslims, 7th Day Adventists, Church of God, C of E, Wee Frees, Canadians, they were unashamed of their religion and saying their prayers.
So what, forget the instant outrage at anyone doing something you deem out of the ordinary because, diddums, it makes you "uncomfortable".
Read a book, watch a film, do a crossword, in short get on with your life and let them get on with theirs.