This is a misleading "experiment". Why were only White House channel videos looked at? If you wanted to show that there was targeted dislike manipulation, you would also need to do this analysis on other popular videos, preferably right-leaning political ones. This could simply be an algorithm that detects bot behavior which gets applied broadly, in which case they are not changing any "real" signal.
It's certainly possible that Youtube is acting in a political manner and is preferentially deleting real dislikes, but this post hardly proves that.
50000 people would show up to a Trump rally. 15 journalists to a Biden rally. Engaged dislikers are not "bots". And the left has plenty of resources to have their own like-"bots". No, the truth is very simple. There's at least 50000 Trump supporters that will downvote Biden's white house. Even more because ... no travel required.
My main point is that the article suggests that this manipulation is selective, and while Youtube might indeed be selectively manipulating White House videos, the methodology used doesn't show that.
Here's a simple question which should be easy to answer, if you've actually approached this in an impartial way: does Youtube also remove likes or dislikes from other videos in a similar way? If the answer is "yes", then the conclusion becomes much less politically interesting.
PS, I think you're overestimating the amount of people who care about White House channel videos. E.g. the press briefing from 3/29/21 has less than 34,000 views. I guess some of the Trump rally attendees forgot to show up to their downvote party.
It's certainly possible that Youtube is acting in a political manner and is preferentially deleting real dislikes, but this post hardly proves that.