"I wasn't trying to [create a] media sensation or anything like that, I just saw the indicators [and] the fact there was a supermoon.
"I think most people realise that the moon effects the tides and so forth and that when the moon's that close, of course it's going to have more influence on the planet," he said.
His prediction was not the first thing that came to his mind when, like many around the country, he was jolted awake by the quake not long after 12.02am.
"Our whole house shook and I hit Facebook because I thought 'if it's shaking this much here, where the hell is the epicenter of this thing?'
And I have relatives in the South Island, so I was obviously concerned," he said.
Soon after his prediction came to light, scientists were quick to de-bunk any suggestion of a correlation between the earthquake and the presence of the supermoon.
However, Gray believed that most people accepted the potential for a supermoon to have a greater influence on the earth as being a fact, and he found it "a little bit amusing" that the scientists who criticised his prediction were at the same time, unable to predict the event themselves, he said.
However, it wasn't just the presence of the supermoon that led to Gray's "educated look into the future" about a potential earthquake occurring somewhere near New Zealand.
"I also saw that there was a lot of geo-engineering and a lot of EMFs [electro-magnetic frequencies] going on over New Zealand and that there'd been an earthquake in Italy and in Japan recently so the [tectonic] stress was moving down towards New Zealand."
In Gray's own words, "geo-engineering" refers to man-made weather. Posts on Gray's weather group Facebook page claim EMFs are being used by unknown entities to alter the weather and cloud patterns.
He explained his interest in the weather was spawned by his job as a painter and decorator.
A storm could mean no work for days on end, so he needed to have his 'finger on the pulse'.
He started studying radar images and began noticing 'abnormalities'.
His own research had convinced him of the existence of geo-engineering.
Nigel rejected the notion that he and the more than 6000 people who now followed his Facebook page were "conspiracy theorists".
But his prediction had brought geo-engineering to the public's attention.
"If I do suddenly go missing, you'll know the men in black have got me."