Might well be the rebuilt 455 on the point using a borrowed 452 tender.
This photo also shows a common operating procedure on the RGS of the first class trains (Motors) taking the hole for meets with long freights. This is particularly true of spots like Brown and Trout Lake where the water tanks are on the mainline. The meeting freight crew can line the Motor in and out of the siding while the engines water up. Another example were several vest-pocket spurs, like Smalley in Lost Canon where a Motor could duck in out of the way of a freight holding the main and flagging.
These meets could be established by train order, "No. 376, Motor 3, meet Extra 455 West at Smalley, No. 376 take spur at Smalley," but, due to the lack of open telegraph offices, and the dynamic nature of the freight train's operations, it would be more likely sticking close to the Time Table and flagging the Motor into the hole.