Is this ->> an old operator or a typo/error?
It looks like a problem in the transcription process. There is a similar problem in DR 42, where the greater than sign is doubled: http://www.open-std.org/jtc1/sc22/wg14/docs/rr/dr_042.html
I learned C in 1992, and I'm 100% certain there was no such operator back then.
From the context, p->>x[5], we can deduce that it appears to do exactly the same thing as the more familiar arrow operator, ->. It is therefore likely to be a typo.
Alternatively, it could be an encoding issue in transcribing the code into HTML. If you look at the source to that page, you can see it's got a strange mixture of escape codes and literal < and > characters:
<TT><B>#include <stdlib.h><BR>