The author is using a tool designed for landing pages. The quality of the samples are going to be wildly different and that needs to be taken into account.

Linkedin calculates an ad impression (last I checked) as 50% of the ad is on screen for at least 300ms. I can be scrolling as fast as my thumb will flick down my LinkedIn newsfeed and it would probably count.

Then the KPI being used is clicks. I don't know of any business owner who would take that as valid. It should be some kind of conversion event (newsletter signup, contact request, or purchase, etc.)

If it were up to me, I'd want 4,400 clicks and a few dozen conversion events to do my calculations on statistically significant effectiveness. Especially since the author is paying CPC (cost-per-click)... who cares about impressions at all?