1. Dinar and dirham are recognized by all countries in the world, while there are many countries still not recognizing Bitcoin.
2. Dinar and dirham have been proven to have stable prices, while Bitcoin's price is volatile or unstable.
3. Dinar and dirham are backed up by an institution, while Bitcoin is not backed up by any institutions.
We cannot conclude that Bitcoin is a digital gold based on some people's opinions. It should get a legitimation from many parties.
However, I don't say Bitcoin cannot be a digital gold but I think it is too early to equalize Bitcoin and Gold.