I'd have a close look at the brass, particularly the case head and necks. There is something more at play than 2 grains over max., are you sure about the scale being off?
This is what my first impression was. A 2 grain overload, while not a good thing, seems like it wouldn't be enough to do what you're describing unless you were already at the high end of the "safe" range to begin with.
Had the case been annealed since its last firing? If so, are you confident it was done correctly? Re-reading your post, I see it was new Nosler brass. Was that the first case of that batch that you've used, or was it a random occurrence?
Either way, I'd be pulling bullets from any remaining rounds loaded in that session and checking charge weights, as well as taking a hard look at any other variables you can think of.
I've had very limited experience with loading .223, so take this advice with a grain of salt. I've heard others say that small capacity cases like the .223 can be finicky to load compared to .308, for example.
I guess what I'm trying to say is, don't hang your hat on a 2 grain overcharge as being the sole cause of what happened until everything else has been ruled out.
I don't like playing with the high end of a particular load either, I'm more comfortable with a moderate load.
I take it the Viht 133 is part of a published load that you've used in the past?