Must have been taken just after some large trade. Here are my samples from the time around my post (timestamps in CET):
20:12 mtgox premium over bitstamp is currently 9.43015538326 %.
20:53 mtgox premium over bitstamp is currently 9.80714742711 %.
22:18 mtgox premium over bitstamp is currently 9.15855226897 %.
Currently:
07:18 mtgox premium over bitstamp is currently 9.95425434584 %.
Far below the 12% to 14% from a couple of days ago.
That is a lie. Those numbers are completely fabricated, or chosen as the lowest values in a minute by minute range. Mt.Gox/Bitstamp variance hasn't been lower than 10% since 8/9.
These values were taken from Bitcoincharts.com. Would you like to provide your source? I'd love to see it.
I thought my source was well known, and I already provided it. gribble is a bot in #bitcoin-otc and other Bitcoin related channels on freenode. It fetches the tickers from both exchanges and calculates the difference. It works with several exchanges. E.g:
09:35 ;;premium bitstamp btce
09:35 bitstamp premium over btce is currently 2.01656900384 %.
The samples were taken at random times. The samples in your graph seems to be very far apart, and is certainly not accurate enough to prove anyone a liar.