Its funny you talk about sampling error while agreeing with a gentleman who did exactly the wrong thing to shelter from lightning (against a rock/granite cliff in a puddle of water). He would have been better off to continue riding. And regardless of the actual probability of a lightning strike, it is clear that riding in an unsafe manner as described by the OP in poor visibility conditions is likely to be much more risky...

So again, seek shelter as soon as possible, but do so while continuing to ride safely...