They are talking about millions worth of BTC in USD not millions of bitcoins. There are quite a bit more than 5 out there. According to
this article there are more than 93 thousand out there holding more than a million dollars worth of BTC. It wouldn't be surprising if many of these folks were members here at one point and maybe there's even a few lurking around or participating here and there.
Just one problem with that article, it confuses Bitcoin addresses with "accounts". So people with more than 1 address with over 1m USD value are being counted too many times, eg. Satoshi is being assumed to be approximately 25,000 people.
I do agree with your basic point that Bitcoin has made many people millionaires but it's likely to be somewhere far higher tan 5 and far lower than 93,000 (so far).