Are you sure it's 20 years? I don't think selling more than the registry max limit (10 years) is allowed by the registry-registrar agreement. Also you should never renew for the max period, because you lock yourself in with your current registrar for at least a year (to transfer your domain name to another registrar you need to be able to renew it for at least 1 year, which you can't do if you renewed for 10 years). Being locked in with a registrar can be risky
They are saying they have owned the domain for more than 20 years, presumably paying much less than 23$/yr during that time. Now they renewed their ownership and they find the price exorbitant.
I did not know about the requirement about being able to renew the domain for transfers, I was considering buying a .com for a long duration but maybe I'll hold off on that.