I can't tell. You may need to see a professional tax advisor. And your question is confusing.
First, cryptocurrency is treated as a capital asset like other collectibles, gold coins, etc. You have a capital gain when you sell for more than your purchase price.
Then, you say both "non-resident" and "working in the US." Which may be contradictory.
If you are working in the US more than 183 days, or you pass the other parts of the substantial presence test, or have certain types of Visa, then you are a US resident for tax purposes. If you are a US resident, then you report all your world-wide income and pay US tax on it, so your gains from BTC will be taxable in the US no matter where you sell them. You would get a credit if you also pay income tax in your home country. https://www.irs.gov/individuals/international-taxpayers/substantial-presence-test
To be a non-resident you must not pass the substantial presence test, or be in the US on certain types of Visas. If you are a non-resident for tax purposes AND you were in the US less than 183 days, then any capital gains you have are not taxed in the US unless the capital gain is connected to the business reason you were in the US (which it probably was not.)
However, if you are a non-resident because you don't pass the substantial presence test or because of your Visa status, but you were in the country more than 183 days, then I can't tell what your tax is if you sell your BTC in a foreign exchange. It would definitely be a taxable gain if you sell in a US exchange. But I don't know if you can make it non-US income by moving it abroad. The similar situation would be if you bought gold coins or diamonds or some other asset in the US and then sold it abroad. I can't find the law on that case, but that's the same rules that would apply to BTC. So if that's the situation, you should consult a professional tax advisor.
https://www.irs.gov/pub/irs-pdf/p519.pdf
