It does seem pretty strict, but without some sort of baseline this might be rather normal. I've never worked in recruiting or seen hard numbers on this sort of thing before so I have nothing to compare it to.
For CircleCI, their new candidate to screen is 25%. This is higher than the 17% average. Their screen stage looks considerably larger than I've seen at most companies: it's 4 different steps. From the 250 candidates, it looks like 7 go into an onsite. That's about 3% which is significantly below the 32% benchmark. Of those 7, 3 will receive offers (it's not mentioned how many accept those offers). So the onsite to offer is 42%, which is higher than the 31% average. We can't determine the offer acceptance from the data.
I think it's great they're looking at the funnel and conversion rates. Most recruiters aren't able to tell you these figures which is a red flag. The only way to improve those metrics is to know them first and then measure how changes impact each stage.
[1] https://medium.com/@jmtame/surprising-insights-from-talking-...