Nope. That has nothing to do with it. However it is a bit of a pickle to explain why so please bear with me.
Vicarious is third party. If a "worker" gets sued and his "employer" does not have training in place. Then the "employer" falls under vicarious liability. If the employer trained the worker. The worker takes all the blame and gets sacked for gross miss conduct. To get technical it is strict, common law Respondeat superior. Translated as "let the master answer"
To answer the original question and provide some advice....
What does apply here is a simple case of common law. You would have to prove violation of duty of care. The claimant must be able to show a duty of care imposed by law which the defendant has breached. Then of course the claimant would have to get past a defense of Volenti non fit injuria ("to a willing person, injury is not done"). Geocaching is inherently dangerous. Prove otherwise or leave the court room empty handed.
So basically without getting really complicated. Based on the "balance of probability" the defendant is going to have put out a pretty stupid cache to get sued. Right now there is no legal precedent that I am currently aware of to tip that balance.
That is the right idea!
Or to put it another way if the landowner has done a quick risk assessment and implemented plans so far as is reasonably practicable to safeguard others then quite frankly the landowner protected too. Adding a cache does not change this basic legal principle.
I hope that all kinda makes sense as I type it at this late hour. In short we are all safe for now.