First a disclaimer. The most difficult questions to answer are ones that ask what someone else was talking about with no solid quote.
But to give you some info - the MoneyChimp Compound Growth shows that from Jan 1, 1934 through Dec 31 2011, the S&P return was an average 12.14%, and the CAGR (compound growth rate) was 10.49.
Given that I've been invested in an S&P fund for my near 30 working years, and its expense ratio is .05%, I've seen a return of about 12.09% over that same period. So I find it unremarkable that some fund performed as well as this less another .17% or so.
You should also know the average and the CAGR are not the same. Simply put, an up 20% one year and down 10% the next is an average 5% return, but 3.9% CAGR. (1.2 * .9 is 1.08, and 1.039*1.039 is the same 1.08)
All that said, there is no guarantee the future returns will mimic the past. If you count on 12%/yr (or 10 for that matter) you will under-calculate the lump sum needed to retire 40 years hence and worse, risk not reaching that goal. But. Plan for 6-8%, as as you get closer you'll be able to easily adjust savings down to not retire with "too much." Waking up to find you're 55 and are 20 years away from the savings goal is "bad."
I probably answered the question I heard rather than the one you asked. I hope you learned something useful nonetheless.