Well, that guy was a Pastor (Preus I believe) and had some very valid concerns. Praying with other religions is not something we should do very often, if at all, in public. Many of my pastors growing up would either offer up the opening or closing prayer and not be on stage (or whatever) during the “group prayer”, or visit the family or families discretely and privately. One old pastor I knew said that such events were often more about the pastor’s ego rather than the family and victims’ souls.
Preus was, and still is, the south bound end of a north bound donkey, and the rest of the synod pretty much knows that. He has been trying to get elected as president for a few decades now, and manages to unite the opposition against him.
The Atlantic Dixtrict lost some of its members in the NYC attack, so there was a direct pastoral need for participation, as with the nearly parallel situation (including charges, later withdrawn) after the Sandy Hook school shooting. I believe the LCMS Pastor lost two young parishioners in that violence.
In both cases, the pastors offered overtly, non-generic prayers and brought the witness of orthodox Christianity into what would otherwise have been a “COEXIST” pep rally/group therapy.
The offense wasn’t in offering a Christian prayer in the presence of non-Christians, but in participating in a non-Christian religious ceremony after announcing himself as a member of the LCMS clergy.