From 1949 to 1989, the stock market averaged 7.2% annually. Saving and investing only $20,000 per year for those years would net you about $5m at the end.
The BLS CPI calculator puts $20k in 1949 at $198,565.55 today.
Anyways, him being a lawyer pretty much answers the issue. You don't usually call any professional job a 'normal job', and that clears it up. It's pretty likely that even then it took some high risk/high reward investments or some lucky real estate buys in the meantime to drive it up that much.
Which is not to disparage the achievement of saving $5mil pre-retirement (or even at retirement) age. It takes above average fiscal discipline and money management to do that even with above average income.
My original point was just that a compound interest savings account isn't that amazing. You have to do more than just sock some money into an account to pull it off.