He seems to be a (former) independent contractor rather than an employee/representative, so I think this is more just misguided fanboyism rather than intentional astroturfing/reputation laundering.
Karat is probably the best/fairest you can do for purely algorithmic interviews, but I'm not sure they're even able to do anything else (the parent commenter's experience suggests not).
I would also consider it more of an exam than an interview - the process is very standardized and sterile, and obviously since it's being outsourced there is no way for the candidate to ask any questions about the company.
(disclaimer as well: went into the interviewer onboarding with them as a contractor but dropped out as I wasn't comfortable proctoring tests that I myself wasn't an expert at).
Hello I work at Karat in engineering (have had a great experience so far). I will make sure someone hears about this. I know there is some degree of customization in the format/content of interviews but sounds like it wasn't to the degree it was advertised which is unfortunate.
What a contrast this is.