I'm not sure the linked data is correct. The charts from the 2012 SHEEO report [1] shows revenue/student increasing from $10,869 in 1991 to $11,095 in 2012 (these are 2012 dollars).
I think you're right, something's wrong with my source.
I'm not sure the SHEEO number's usable "raw", as it uses its own ad-hoc inflation calculation (HECA) instead of CPI or GDP, but even correcting for that I can't reproduce the numbers in the NCHEMS site from its supposed source.
According to this http://www.higheredinfo.org/dbrowser/index.php?submeasure=68... total inflation-adjusted revenue per student went from $5,846 in 1991 to $11,016 in 2011.