[schlumpf]

The press release hints strongly at their toolkit:

> improbably successful trading

Even before considering trading volume they can look at in-the-money trades as a proportion of total trades. Then I expect they would look at smaller denominators to see if timing correlated with the announcement cycle. The use of short-selling would have made it (relatively) easier still to pick up: assuming the company was ~200MM market cap at the end of 2014, of which 28% was held by management and their strategic shareholder [proxy statement 20150417], borrow could have been expensive enough to limit the holding periods of short trades.

As you and other commenters have pointed out, simple screens can indeed be effective. A short-term, infrequent trader (or small group of traders assuming, um, collusion) with a high win rate and presumably high risk-adjusted return would stick out.