The NDP vote in BC save 2001 has actually been pretty consistent since 1972 and their best showings as shown below were actually elections they didn't win.

1972 - 39.59% (won)
1975 - 39.16% (lost)
1979 - 45.99% (lost)
1983 - 44.94% (lost)
1986 - 42.60% (lost)
1991 - 40.71% (won)
1996 - 39.45% (won)
2001 - 21.56% (lost)
2005 - 41.52% (lost)
2009 - 42.15% (lost)
2013 - 39.71% (lost)
2017 - 39.86% (pending)

So NDP numbers are pretty steady is more how the rest splits and where the votes are located that matters.  This time unlike others they gained in the right areas.