Oh, Mistwell, you're exaggerating. (I'm his DM)
This is your first near TPK. You had two other tough fights, but there was little chance of everyone dying. Maybe one or two of you...
The dead rising encounter was WAY too hard for 1st level characters. The party did have a decent amount of bad luck. All of the monsters rolled high on initiative, beating everyone but the wizard and the ranger. So, the party didn't really have time to get into any sort of tactical formation before being boxed into a very small space.
After the first boneshard exploded, I realized I was definitely going to have a TPK on my hands unless I made some quick adjustments. So, I eliminated the final explosion, and just had the explosion when they were bloodied. Even with that, the monsters rolled fairly well, especially on their explosions (2 crits)
The steadfast position also hurt them, as the skeletons couldn't be maneuvered out of the way in order for the party to get past.
Now, had the party been smarter about it, they would have done better. They didn't make much effort to get the dead and dying away from the boneshards before hitting them with major attacks. So, they had people at the edge of death getting hit for 3d6+4 damage (I still wonder why the damage was 3d6+4 instead of 2d6+3 like they are in the MM).
Overall, this encounter seems like it needs some additional adjustment.