My interpretation is that if I conduct a training course for training provider company Y and one of the attendees is Mr X, the clause just means I can't then after the course (for a year) ring him up and say "why not hire me directly for training rather than go through Y".
I certainly wouldn't breach that.
However if I got a call 6 months later from a colleague of Mr X, wanting to hire me directly for training because Mr X had recommended me to them, is that restricted? The lead has come indirectly from my training that first course, but is the colleague now a new client? (Hence my question is a "client" specifically the person on the course, or could the training company claim it applies to the client company in a wider sense)