Well... Hate to be a "bigot", but....
The group was not only a strongly religious group, but religion figured quite largely into the reason for their violence, therefore it WAS about religion.
Perhaps it wasn't a mainstream form of Christian religious practice, but the main reason behind their madness was in fact their special brand of religion.
Now, that doesn't mean that they are representative of the rest of Christianity in any way, but you can't accurately say "It wasn't about religion".
And, as for the part about militias, well, I'm afraid that's pretty wrong too.
Militias are groups that are supposedly prepared to fight the US Government, once the Government crosses a set of predetermined boundaries that the militia group has abitrarily set up.
That set of boundaries differs from group to group.
In this particular instance, the groups boundaries had to do with religion more than government overreach, but government overreach was one of them.
This family didn't attend a church apparently. While they may have justified their actions and intentions using the Bible, I don't think that makes them religious. Using religion gave them a sort of moral justification in their minds, not reality.
If I call my group the Democratic Party Militia, does that make us Democrats?
Their target was local police. Translating it into a federal level seems a reach. It sounded like they expected other groups to rise up and tackle that one. I interpret local police as teh target, to mean they were against local authority figures.
Seems the leader once shot at local game officers and felt enboldened to keep other authority figures out of his life by attacking at this time.