Yes I have seen that, but I understood this was the traditional reception for the compatriots in the country the royals are visiting. In all State Visits, by Sweden, by Norway, by Spain, by the Netherlands etc. there is always a reception with their respective communities, usually on the second or third day of a State Visit.
My impression of that event in Hamburg was exactly the King and Queen Camilla meeting British compatriots whom have made a living or are entrepreneurs in Germany.
I have not understood this was a return event to their German hosts which usually is a banquet, or a concert, or a ballet, or a theatre performance, on a representative location, packing out with all glanz und gloria.