First, the fellow who wrote it was never Christian, so Christian Millenarianism wouldn't be ingrained into him.

He was born and raised in a predominantly Protestant Christian society, where these beliefs are widespread. And, by the way, apocalyptic beliefs existed in all religions and cultures, including Judaism (Christianity was originally a messianic and arguably apocalyptic Jewish cult).

Second, 'Beyond the Reach of God' doesn't aim itself back into religion and less still Revelations-style religion. 'Let's build a tool that makes life fair' is completely crosswise to any religious teaching.

'Salvation through good works' comes to mind.
More generally, various doomsday cults have beliefs involving the cult members having to perform specific actions in order to trigger the Apocalypse or make sure that it unfolds in the intended way.

I don't want to push the pattern-matching too far. 'Singularity is a cult' has been already debated at nausem here, and is probably and exagerated position.
It sufficies to say that singularitarian and religious ideas are probably salient to the same kind of psychological mechanisms and heuristics, some innate and some acquired or reinforced by culture.

As I said in the my original comment, this doesn't necessarily imply that singularitarian beliefs are wrong, but it strongly suggests that we should be wary for availability heuristic/priviledging the hypothesis biases when we evaluate them.

When you have two ideas that are: called differently, they claim no common origin,

'Beryon the reach of God' seems evidence to the contrary.

one came from revelation while the other from reasoning presented publicly,

Fair enough.

one claims certainty while the other claims uncertainty,

Does it? I'm under the impression that singularitarians believe that, barring some major catastrophe, the Singularity is pretty much inevitable.

one is a moral claim while the other is a factual claim,

No. Both are factual claims about events that are expected to happen in the future. They may be more or less falsifiable, depending on how much the authors commit to specific deadlines.

one is supernatural and the other is materialistic...

Any sufficiently advanced technology is indistinguishable from magic.