> He spent 1,000 DASH / (4,000.00 [USD/BTC] / 300.00 [USD/DASH]) = 13.(3) BTC

Maybe I'm calculating this incorrectly, but using the above, I come up with a cost of 75 BTC for 1000 DASH. And given the current BTC price of DASH at coinmarketcap.com[0], I see 1000 DASH would run about 55 BTC.

Either way, it's certainly possible that the purchase was for diversification, if one speculates the initial BTC "basket" was quite a bit larger.

[0] https://coinmarketcap.com/currencies/dash/

I really screwed up my math, thanks for checking.

Order of magnitude sanity check is ~10 dash for btc, so 1,000 Dash should be on the order of 100 btc.

I don’t follow. He shows a balance of 1000 DASH (=300k USD) in his wallet. How is it related to the price of BTC?

I think the point was that he probably already had a significant cryptocurrency investment portfolio. He isn't really spending money at this point, simply diversifying his portfolio.

Diversifying his USD portfolio would be much the same IMHO.

People who pay taxes in USD tend to use USD as a numeraire. IIRC in New Hampshire you can pay taxes in BTC.