I never heard of any "Calvinist" (or any Christian, for that mattter) who says "Bism'Allah, alrahmen alraheem ameen."
Maybe they were Calvinists years ago, but I think this is MSM spin to cover up Islamist sympathy.
The Bergdahls are Presbyterians, and most Presbyterian denominations are WCC apostate. The WCC used to give money to national liberation, i.e., leftist guerilla groups and now support abortion, gay marriage, and the whole globalist agenda. They may give lip service to the Westminster Confession, but that is the extent of it.