This is not even remotely true. Please point to any legitimate insurance provider that has this exception.

There isn't a written exception for it in the policy, but when the claims adjuster comes round they'll use it as an excuse to not pay anything because there's no evidence of theft.

Depending on the value of the claim, if you believe the lock was picked, there are people/companies that can check the lock for forensic evidence of that [1] since picking, raking or bumping leaves very different marks on the pins than normal key usage.

[1] https://www.blackhat.com/presentations/bh-usa-09/DATAGRAM/BH...

Questionable if it's not in the insurance agreement.