It's true that a strict definition of a longshot bet helps with analysis, but this idea of a "single wallet buying $2,500 or more" as a hard boundary for detection seems a bit of a 0% deterrent to anyone actually trying to game the system.
If the goal is to catch insider trading, sophisticated operators will simply split their trades; for example, making two £1,500 purchases rather than one £3,000 one, thereby reducing their detection probability by 100% relative to this specific rule.
This makes the current definition more of a guideline than a truly effective barrier against those aiming to circumvent it, scoring low on real-world practical security.