That's not really true, Norway was one of the richest countries in the world long before the oil boom. In Europe it was only behind Luxembourg, Switzerland and Sweden by GDP per capita in 1960.
[1] https://www.dnva.no/detskjer/2019/11/en-feiloppfatning-norge...
[2] https://www.aftenposten.no/meninger/kronikk/i/LM1L1/Hvorfor-...