Yeah, kufr (fabrication). You have my work on the matter in a thread called 'Nearness and Guidance' including an astonishing revelation about salateh.
However, Musalla can refer to a gathering in a temple (church, mosque, synagogue etc). It is only that it refers to guiding/teaching/giving perception in there and not a ritual. Sectarian confusion probably emerged when people begun to equal musalla with prayer and eventually it turned into being synonymous with prayer. The Christian word 'Divine Service' is slightly more accurate. Communion is a really good word, check a dictionary.
But one should seriously draw a distinction between to pray (du'a) and a guiding session (musalla). If a cleric has a lecture in a temple then he holds a musalla and the participants gain salateh (guidance/perception). Should he begin to pray then it is du'a, even if it is during the musalla. It is so obvious.
One has a clear example concerning the alleged "praying birds" in Quran. Do they pray in midair or are they following each other in formation up to a leading bird and the leading bird is following the perception of GOD? Musalla (which gives salat) is following the same principle as the parable, i.e. someone is guiding the other.
And a blind man cannot lead another blind man. (Old parable)
Salaam