From the article:

>Specifically, every two seconds they predicted the average price movement over the following 10 seconds. If the price movement was higher than a certain threshold, they bought a Bitcoin; if it was lower than the opposite threshold, they sold one; and if it was in-between, they did nothing.

If they are indeed predicting the price at X+10 seconds at second X, they have more than enough time to act on that info without having to do HFT.