Wont be able to access the Chromebook for a couple of weeks. He kept it in a Safety Deposit Box and the bank won't holds it for 30 days with a proof of death. Hopefully it will show something.
Do you know if he always stored his Chromebook in a safety deposit box with his bank? If so, it seems (to me at least) a probable solution as a cold storage method with the two strings being the password for the computer and the other for his wallet.
It doesn't look like any private key I've ever seen, nor does it seem to be a seed necessary for recovery of a wallet.