Does Bitcoin meeting a dictionary definition of a currency (that is being a medium of exchange) really matter given his actual point (which you've clearly understood)?
Also, if your defence of Bitcoin as a currency is to compare it to the Zimbabwean Dollar (a currency ridiculed and later abandoned) then is it OK if I ever need a lawyer that I pass on you and go to the next guy? ;-)
His primary point of view is making money. If I can't figure out how to make money on something, I will dismiss it. This is likely what he is doing ATM, but not a good assumption moving forward.
I don't think he's dismissing it for all time, he's just raising a valid point about it as it stands right now.
I don't read what he's saying as anti-Bitcoin per se, he's just saying that right now the massive variability around it means that it's not really a functional currency. That's a valid view and not one he's alone in holding - most economists, hell most people, whether they're pro or anti-Bitcoin will accept that the current fluctuations are problematic when it comes to day to day use.
Also, if your defence of Bitcoin as a currency is to compare it to the Zimbabwean Dollar (a currency ridiculed and later abandoned) then is it OK if I ever need a lawyer that I pass on you and go to the next guy? ;-)