Cryptocurrencies are just considered as 'digital gold' because of its relatively higher price, especially Bitcoin. Aside from that, it isn't really supposed to be considered a luxury asset, but rather still a mode of payment that may be applied on a wide scale of purchases. It's just that Bitcoin couldn't scale, and with it being deflationary (which makes it increase in price over time), makes it a good contender in handling macrotransactions, and that includes luxurious products. If Bitcoin could scale, then it wouldn't be seen only as digital gold since more people could actually use it, whether it is priced low or high.