Clearly that isn't fresh 4831, or at the very least not normal serviceable 4831. So while it may be fair to say that good 4831 can't normally produce pressure problems from Nosler load data, very clearly that isn't good, or normal 4831.
Also None of Noslers data online indicated that it is a compressed load, only Hodgdon shows that with a lower charge. Compressed is one thing, being so compacted as to have to chisel or pick it out of the case is quite another. If nothing else that should have been a huge red flag while loading.
Now if we pretended that the powder wasn't messed-up like it is in terms of size, shape, geometry, and what looks like obvious construction differences. Then to be found so compacted as to have to pick at it to get it loose, I have to wonder...
With that level of compaction, clearly designed-for burning rates can very easily go out of the window. How many times have we read about or discussed slow burning powder charges and or fused powder charges detonating?
I would also wonder about some type of hang-fire event where he didn't wait for it. If he began unlocking the bolt and then that fused mass of powder let go in an uncontrolled way, then the results can speak for themselves.
Cheers