This actually sounds a lot like an urban legend. Especially given that it’s a story you heard in your youth.
I wasn’t able to find a report of that happening at the Hofn station, but the same story of this happening to an anonymous microwave technician does appear in other locales.
Yep... considering the skin effect, any microwave radiation would start heating the outside skin layer first, and it would hurt long before anything inside you was "cooked".
If you got locked in there.. then sure... maybe.... but staying in there and not feeling it (or just feeling "warmer", until you die...) nope.
I wasn’t able to find a report of that happening at the Hofn station, but the same story of this happening to an anonymous microwave technician does appear in other locales.
Snopes did a debunking on these and they say it’s false: https://www.snopes.com/fact-check/nuke-of-earl/