Nice picture, Tom.
I believe this is a picture may have been the last run or very near the last run of the abbreviated San Juan that ran between Chama and Dulce in 1951.
The coach added to the consist is very rare for that train.
As for the reefer, these cars were used for LTL freight on freight trains, and were probably also used for LTL in the rare event that it was needed during the life this run between Chama and Dulce. There was only one active baggage car left on the roster by this time, and all of the RPO's were effectively decomissioned, so the reefer is standing in to handle extra baggage.
The Combine #212 was usually if not always run backward Westbound, presumably because there wasn't anyplace sufficiently long enough to turn the train between Chama and Dulce.
In this picture, the train is Eastbound just past the Chama Depot and was made in the morning (note shadows) as the train was being switched to the Depot.
To answer your question, this was still considered a passenger train on the D&RGW and operated with the San Juan train numbers, #215 and #216, so it was not an official mixed train, despite its odd consist.