I am actually trying to better understand the distinction between mixture models and mixture distributions in my own work. You seem to say mixture models apply to a small set of models – namely regression models.
“Finite mixture models have been used for more than 100 years, but have seen a real boost in popularity over the last decade due to the tremendous increase in available computing power. The areas of application of mixture models range from biology and medicine to physics, economics, and marketing. On the one hand, these models can be applied to data where observations originate from various groups and the group affiliations are not known, and on the other hand to provide approximations for multi-modal distributions.”