You will find that many yard owners these days will ask for proof that a horse is insured, it's mainly because their insurance companies will ask for all equines kept there to be insured and at the end of the day, if something happens while you aren't there and your horse is liable, the yard owner needs the insurance details. I won't have a horse on my yard without having a photocopy of it's insurance. 

All I would give him is the name and numbers of my vet and farrier and who to contact in an emergency.  I would also provide details of when the horse was vaccinated and wormed, but your insurance details are your private business.  All he needs to know is that there is an insurance policy in place, if there is ever a need for a claim to be made in his opinion then he lets you know and you can deal with it yourself.