He's right that Bitcoin isn't a unit of account since people price their goods and services in USD/EUR to BTC rates rather than Bitcoins themselves. Would you intuitively know how much a coke is in BTC? I bet you can do it for your local fiat currency though.
I should continue the criclejerk though: He say bad about Bitcoin, he bad! He know nothing!
But to say bitcoin isn't a 'unit of account' because people don't price goods in it - is just plain stupid. 'unit of account' has far greater meaning than 'people price goods in it'. A professor at Columbia should not be arguing that because goods are not priced in bitcoin, it is not a unit of account. Furthermore, people are beginning to price things in bitcoin - without regard for dollar or euro equivalent. In one example, Mastercoin just raised a shitload of money on the notion of 1BTC = 100MSC - with no regard whatever for the value of dollar. There are many more similar pricings each day. But these are not necessary in order that bitcoin be considered a 'unit of account'.