I’d push back on this framing a bit. There's a subtle ageism baked into the assumption that someone who stepped away from day-to-day coding has "ancient skills" worth mocking.

Yes, specific frameworks and tooling knowledge atrophy without use, and that’s true for anyone at any career stage. A developer who spent three years exclusively in React would be rusty on backend patterns too. But you’re conflating current tool familiarity with engineering ability, and those are different things.

The fundamentals: system design, debugging methodology, reading and reasoning about unfamiliar code, understanding tradeoffs ... those transfer. Someone with deep experience often ramps up on new stacks faster than you’d expect, precisely because they’ve seen the same patterns repackaged multiple times.

If the person you’re describing was genuinely overconfident about skills they hadn’t maintained, that’s a fair critique. But "the actual engineers making jokes about his ancient skills" sounds less like a measured assessment and more like the kind of dismissiveness that writes off experienced people before seeing what they can actually do.

Worth asking: were people laughing because he was genuinely incompetent, or because he didn’t know the hot framework of the moment? Because those are very different things.