That is specifically related to leaving your car unlocked when you leave it.
The original poster said that your insurance doesn't cover you if your car is unlocked. That is not true, it is often unlocked when driving or getting out of the car.
The clause doesn't mention unlocking the car by someone else either.
There seems to be constant myths about insurance companies that they can just not pay out whenever they feel like it.
I would say to the person who said "sorry sir, your claim is invalid" to show me where it says I can't allow a third party access to my vehicle. I took the keys out when I left and locked all the doors and windows.