They find that most millionaires are quite frugal, have stable families, and live modest lifestyles--they have accumulated wealth but don't flaunt it and don't waste it. These are essentially the lowest risk strategies in life, and survivorship bias favors the exact opposite, i.e. the "lottery ticket" decisions.
The exception to the low risk mantra is that many millionaires run their own businesses, and of course entrepreneurship is risky. The authors do note the effects of survivorship bias here.
I'd summarize the book by saying: "work hard, live well below your means, and invest the difference. Also, don't spoil your kids if you want them to build wealth."
From the "Millionaire" or not game we're all "losers" by default.
On the other hand, a low risk strategy might give you a comfortable life with high probability, but almost certainly won't make you a millionaire.
You need to know the base rate to understand whether survivorship bias is a factor or not.
If you invest $5k per year and earn a 7% annual return with a mix of stock and bond index funds, you'll be a millionaire in 40 years. If you don't like my 7% number, then invest $16,500 at 2% (short term government bond type rates), and you'll still get there in about 40 years.
For a sufficiently frugal person on an engineer's salary, getting to a >$1 million net worth is easy, but it takes a while. It's worth noting, however, that $1 million isn't a particularly lavish retirement anymore (and will be much more modest in 40 years).
The easiest way to become a millionaire is to have boring financial habits.
I have not read The Millionaire Next Door, but that seems fraught. Does it avoid survivorship bias? E.g. Playing the lottery is a 'habit' common to all lottery winners, but it's also common to all lottery losers, of whom there are many more. If you only studied the winners though, the lottery might start to look like a wise investment. Maybe the habits common to millionaires are counterproductive for the average person and only helpful to the lucky few.