My stats are taken from fangraphs and statcast. I don't think comparing a 6 year veteran players career average against his current o-swing is a very reasonable way to compare his current statistics for what it's worth. You seemed to have cherry picked the worst plate discipline numbers for Grichuk of the multiple available metrics to make your case, but by all of pitch f/x, pitch info and statcast Grichuk has set a career best marker.
Perhaps a more telling stat is his o-contact percentage, this is a much more sizable increase of up to 15%, that could be behind a lot of his increased success, with less swing and miss/more foul offs etc.
Grichuk hasn't lucked his way into his current numbers, he is being rewarded with results consistent with his quality of contact. His .395 woba is consistent with a .391 xwoba. He isn't simply fluking his way into a bunch of wall scraper home runs, he is making consistent hard contact and reaping the just rewards. Check out his statcast page, Grichuk ranks:
78th percentile in hard hit%
81st percentile in xwoba
90th percentile in xba
87th percentile in xslg
89th percentile in barrel %