They are probably lying. It's likely Bin Laden died back in December 2001 from lack of access to kidney dialysis (he had bad kidneys, and didn't exactly have access to good medical care while on the run).

But that didn't jive with the powers that be, so they propped him up as a real-life Emmanuel Goldstein. Notice in the videos over the years, "Bin Laden" never really looked the same way twice.