A close group of cyclists may be normal in one triathlon and a rule violation in another. Before copying what you saw in an elite race, establish which rules apply to your own event and category.
World Triathlon’s rules FAQ distinguishes draft-legal and draft-illegal formats. The event’s current competition rules and athlete guide provide the applicable details. Distance, category and organiser matter; a remembered number from a previous race may not be enough.
Read the passing sequence, not just the gap
A non-drafting rule normally involves more than staying a certain distance behind another rider. You need to know how a draft zone is defined, when you may enter it to pass, how long the pass may take and what happens after you are overtaken. Blocking and vehicle-related restrictions can be separate issues.
Write down the exact rules from the event documents and their version date. If the guide and another source appear inconsistent, ask the organiser before race day rather than choosing the more convenient interpretation.
Practise a decision, not a penalty calculation
In an appropriate, safe training setting, work on observing traffic ahead, making controlled speed changes and returning to a predictable position. Ordinary road laws still apply outside the race; a race-course passing rule is not permission to ride unsafely on public roads.
For your race briefing notes, include three prompts: what constitutes a completed pass, what you must do after being passed, and where any penalty must be served. Understand the official instructions instead of assuming a marshal will explain them while you are riding.
Draft-legal racing also has equipment and conduct requirements, so “drafting allowed” does not mean there are no constraints. The useful preparation is to arrive with the right rule set, suitable equipment and a riding plan that does not depend on guessing what the rider in front intends to do.