Since Bitcoin is by definition, deflationary, because it has a limited supply, it will supposedly have more purchasing power over time (assuming good adoption and acceptance of bitcoin). Bitcoin is limited to 21mil forever. I quote from the course,
Many economists argue that a deflationary economy is a disaster that should be avoided at all costs. That is because in a period of rapid deflation, people tend to hoard money instead of spending it, hoping that prices will fall. Such a phenomenon unfolded during Japan's "Lost Decade," when a complete collapse of demand pushed the currency into a deflationary spiral.
Tour first mistake here is without providing a link to this aspect quoted by you, this will give us proper check in understanding the right channel the author was addressing wjen saying that that a reflationary economy is a disaster, ours here is a digitally decentralized network with bitcoin and it was not stated that bitcoin is what was being referred to here nor a digital economy, the word deflationary can be used on different contexts, the reason why i said you would have provided the link for referencing this article you posted.
Now what would happen if people did start suddenly hoarding?
Have you even consider the fact that bitcoin is a currency anyone can spend digitally, which means the global distribution of bitcoin isn't limited to a certain place or some caliber of people, there will also be a demand and supply as long as it existed, those hoarding won't do that for life, they more they release the lower the price the higher the demand which will also geared up the price to surge higher as the demand increases.