One who buys only 900 USD worth of merchandise with 1 BTC obviously does not believe that 1 BTC will be worth 10,000 USD in 2015...
What is that supposed to mean - We're all supposed to refrain from using bitcoin for years until it's reached its ideal valuation? You're telling bitcoiners not to use bitcoin? What sense does that make? No thanks. And that's not going to help the btc economy. If nobody used it then it wouldn't be worth anything. That's a paradox!
He's not telling you to refrain from using bitcoin, if you really have to. There are drug dealers posting in these forums that need to use cryptocurrencies,
but the Average Joe (well, assuming he doesn't use illegal drugs) doesn't need bitcoin to do online shopping. Someone who buys now some expensive stuff that
he doesn't really need with bitcoins, through a retailer, has the same effect on the market as selling on an exchange and using the fiat for the purchase.
So he can claim that he holds tight, but he just takes advantage of the opportunity offered by the retailer instead of dumping (the retailer will dump).
I encourage the holders to buy stuff (even what they don't need) with bitcoins, this will bring more coins to the exchanges and the price down.