Better yet, just call it HMS Guardian and piss off the entire range of special interest groups. Make sure it’s carrying Trident.
There was an HMS Guardian - not that the readers of said paper would approve as she was an offshore support vessel (evil capitalists) later purchased by MOD and used as a patrol vessel in the Falklands (fighting a right wing dictatorship - bad).
I honestly don't know.
However, I'd guess that it has more to do with GRP MCMVs being very light, and the blast wave just lofted it slightly. That and the craft are small, so you wouldn't get differential loading in the same way as a larger metal hull.
Also, it's not so much that GRP is brittle as that it can be quite easily torn. Different material structure and properties.
That is enough Materials Science for one morning....