Can I ask what it is you're expecting ?
As I said above the club are not going to accept blame/fault in case it comes back to bite them, I would have expected the individual to apologise when they came looking because that's good manners.
Also try as I might I cannot find anything that actually says it's illegal
Airgun pellets are a specific offence but I know it doesn't apply to shotgun pellets for example
but I can't find any reference to arrows.
Plus if the field where it landed is owned by the same person as the range then while it might have left the range area it hasn't actually left the "property" in which case the only person you could complain to would be the land owner who may or may not care (they might even be one of the archers)