I think your point may be that he doesn't have anything private on the phone to worry about or anything that needs to be kept secure?
I think the argument hidden in the headline here is that since this is a device owned by a congressman, and allowed inside this particular meeting, it has information on it that may be confidential, and therefore needs a much stronger password.
My phone has access to my email, phone number, texting.
With these 3 things you can get into my bank account, access to my domains, and into any online account I hold.
Then, personally and professionally, I manage other peoples' accounts, so, with my phone, you can probably social-engineer your way into those as well.
My point is, if you are married, have a job, email, or have other people in your life that you don't want to go through an identity theft crisis, or get hacked, stalked, etc, you should lock your phone.
Maybe you aren't the target, but you are the wide-open back door into their life.