At any airport around the world it's quite normal that if you are departing or entering a country with more than $10k currency, you have to declare it.
Cryptocurrencies are another matter. What you must declare are banknotes, traveler's checks, gold coins... Anything physical. The future will probably assimilate cryptos to money in the bank, but so far there isn't a single word about
BTC in customs regulations.
Most likely, that's the way it is. Crypto currency at the border crossing is not necessary. In any case, your duties should be stipulated clearly in the customs regulations. Without this, there can be no additional duties.