score:8
Destination distance signs are supposed to be placed
Approximately every 20km between destinations or 40km intervals for highways that lie north of 54° latitude.
Source: BC's Manual of Standard Traffic Signs and Pavement Markings (PDF), chapter 4, page 4.8.
(More resources are available at the BC Ministry of Transportation and Infrastructure's page Traffic Signs & Pavement Markings.)
This highway is just south of 54 degrees north latitude, but I could not find another sign either 20 km west of this one nor 40 km west. But I did find one that is (nominally) exactly 100 km to the east, which appears to have been placed just west of McBride in keeping with the instruction to install these signs
Approximately 200 to 300m beyond the developed area departing an incorporated municipality
I suspect that this is the reason for the placement of the sign that you found.