Some people think that if they look down hard enough at someone else, they can lift themselves up. Especially if that 'someone else' is someone clearly high-status by an agreed standard (which 'senior software engineer at Google' undoubtedly is, on this forum, no matter what we tell ourselves).

So the GP comes on here, sharing a perfectly nice and candid opinion, and our friend sees the chance of a lifetime ("terrible manager", "would never work under you", "management isn't for everyone", "find a higher-quality organisation", etc). Simples.