On the evening of June 19th, 2019, a brief summer storm brought 15mm of rain in 30 minutes. There were several lightning strikes in the area, including this one to the south of the Stawamus Chief.
The video clip is slowed down by a factor of ten. Although it appears that the lightning is striking the Chief, it actually struck south of the Chief (behind it from the viewpoint of the camera), possibly in the area of the Sea to Sky Gondola.
The daily timelapse video for June 19th, 2019 provides an overview of the day, with the storm coming in around 9:00pm. If you look closely, you can also see the lights of a group of climbers just below First Peak at around 10:00pm, only half an hour after the nearby strike.