He spent 1,000 DASH / (4,000.00 [USD/BTC] / 300.00 [USD/DASH]) = 13.(3) BTC. At this point I think it counts more as diversification.
edit: [BTC/USD] -> [USD/BTC] && [DASH/USD] -> [USD/DASH]
edit: [BTC/USD] -> [USD/BTC] && [DASH/USD] -> [USD/DASH]
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.
Order of magnitude sanity check is ~10 dash for btc, so 1,000 Dash should be on the order of 100 btc.