This kind of gloating is lame, because it's the same sort of empty words that the Bitcoin bulls of last year were spouting off. If you really wanted to bet $10K that the price of Bitcoin would be less in a year, you would've shorted $10K worth of Bitcoin on one of the many exchanges that allowed it last December, and you'd be up about $50K today. Similarly, if you want to bet $10K today that it'll be higher in 2019, just go buy $10K worth of Bitcoin. If you're ultra confident do it on margin, and then "not having $10K to bet" is no impediment.

yeah, if bulls had been correct and there was a paradigm shift and Bitcoin soared to 100k this guy would have simply kept quiet about his prediction.

If he was truly confident in it he would have taken out a loan and put it on a binary option for bitcoin to be below X price 1 year later, or as you said gotten a broker account and shorted with 100x margin

Bitcoin (and all the rest) have no intrinsic worth, being merely a series of numbers.

True wealth does not rely on having 'notional' value, but on reality. Thus a rentable property is "real" estate. A ton of iron ore, a ton of titanium, and similar things have "real" value.