Money is technology. 
Discussion
Honestly the portable column is debatable. One ounce of gold is lighter than a wad of $20’s in cash to reach $2k (and much smaller).
If the fiat is in hundreds they are comparable though. Most people are not carrying around bars of gold bullion which is probably what they are referring to in this.
Bottom line if someone needs to travel and bring money, a combo of all 3 is prudent (at least until fiat is so debased that it takes up too much space lol)
Isn’t the fungibility of bitcoin debatable?
Never heard of it.
Every satoshi is not equal. Each one has a different history. At the very least, KYC bitcoin is not equal to non-kyc bitcoin. You can tell because people will pay a premium for non-kyc bitcoin. Therefore, each unit is not a 1:1 exchange with any other unit. Is that not what fungibility is? If you disagree, than I will trade you all of my kyc bitcoin for all of your non-kyc bitcoin 😁