My guess is that when coinbase dipped a big buyer on coinbase put in a huge buy order, this would inflate the coinbase price before any other markets (although with that spread, people performing arbitrage should get it back to normal pretty quickly)
Yeah, they're saying they base their prices on orders on there own site, plus current prices on un-named exchanges. Most of the data for buys and sells on their site are hidden or obsured in low resolution charts. Doesn't this look wrong? lol
http://i.imgur.com/tQwMIfB.jpg