Slugs to be you then, I guess. :P
In all seriousness, the graph shows different species as fraction of total uses recorded. Since the paper is mostly about mice, and behavioural differences under different circumstances, it being unfair to the slugs is probably not such a big deal here.
To be fair, the people at the cutting edge of modern computing are statistically very likely to be Linux users. Therefore it’s not entirely unreasonable to have some prejudice against Linux users.
But as a sweeping measure these anti-cheat measures are absolutely unacceptable. The only other explanation is that they just don’t want to bother with the market share still being low compared to Windows.
Personally, if a game requires anti-cheat, it’s probably not a game I’d enjoy playing. Not a big fan of competitive gameplay. But for those that are, this needs to stop. Especially with all the new bullshit Microsoft has been pulling in Windows lately.