According to that article it has nothing to do with condition, but with the lack of anti-counterfeiting protection on older notes.
I have lived in, and briefly worked in a bank in, in a country where people do use USD, GBP etc. notes as a store of value, sometimes in large amounts (you hear about that when they get burgled!).
Cambodia official currency is USD (1000 riel = meant to be 0.25c, goes up to 50000 riel) prices are advertised in $ in general with sometimes 1$ = 4200/4300/4500...
Anyway key point is your USD better be mint and at least 2018 or they will refuse it... Same at currency exchanges in most of south east Asia that have their own currency.