London day rates I've seen for contractors are more like 700 - 900/day on average at places that pay a bit better and 1000+ for specialists. And base salaries I've seen advertised for senior developers at funded startups (e.g. Wagestream, Truelayer) are more like 105k now (more for higher levelings - i.e. Principal/Staff).
This probably refers to Uber and Peter Thiel and companies associated to him?
If they're manipulating HN they're not very good at it. Lately I'm seeing smear pieces against them appear on the front page on almost a daily basis and the tone in these threads is overwhelmingly toxic rather than positive.
As to day rates I think it's rather about companies willing to pay a bit more to get better contractors rather than any specific stack.