People are more discouraged to hoard their currency, than to let it circulate.
Did you mean to say this? I don't quite get your point here. It seems you are comparing two similar bananas. If the prices of goods and services are decreasing, people won't be hoarding money. Spending would be encouraged because things are affordable. So there will be more circulation of money. On the other hand, another explanation would be that if the prices of goods and services are continuously falling, people would not be discouraged to hoard money. It's because buying in the future is better than buying at present. So there won't be circulation anymore.
The key difference is that people don't foresee a fixed cost (unit amount) that they must pay with Bitcoin. If the value of the Bitcoins that they own increases, then any future cost will take a proportionally smaller amount of Bitcoins. There isn't any fixed incentive to holding Bitcoin other than speculation.
If the economy that uses Bitcoin grows, the per-unit value of Bitcoin proportionally increases also.
Everything is the opposite of the popular fractional reserve banking system (because Bitcoin isn't a debt but an asset). Bitcoins only deflate in value when the Bitcoin Economy is growing.
Because the Deflationary spiral is a real problem in the traditional monetary system, doesn't necessarily mean that it will also be a problem in the Bitcoin economy.
To be honest, I am also confused. I think I will have to reread the entire explanation a few more times before its meaning will finally sink in. Because if this: "If the economy that uses Bitcoin grows, the per-unit value of Bitcoin proportionally increases also." then why this: "Bitcoins only deflate in value when the Bitcoin Economy is growing."