I'm not sure why you posted code here - I don't think the possibility of this code being written was ever in doubt.
Personally, I already said I don't think 99% is accurate, but... we'd have to define terms.
"PHP developer" - is that different from someone who modifies (or creates) PHP code as part of their job to earn a living? Maybe they're just "PHP workers"?
The very notion of "array_shift" and "array_push" is foreign to a non-trivial amount of PHP workers.
The word fibonacci is foreign to a hell of a lot of people who make their living in code.
I don't think you interact with beginners/amateurs enough to understand where pc86 was coming from.
If you describe fibonacci in english, gave some working parameters, I would be willing to bet 15-20% of people who self-identify as "PHP developers" (and get paid a wage for it) would struggle and ultimately fail that test above.
I still see code (not a lot, grant you) where people have not understood what passing a parameter to a function call means, and instead the first line of each function call is a string of "global $foo" stuff.