He was contracted to make a synthetic dataset, based on a small set of records which were supposedly randomly sampled from a larger original dataset. He didn't really have any way of knowing he was being lied to at that point, or what his work would be used for.
But when he invoiced $13k for his services, including a detailed breakdown of what he did, Javice came back and offered him an extra $5k if he would change the invoice to a one-liner that just said "data analysis services". And he immediately agreed.
I find it hard to believe someone could get that request and not understand that they were being asked to be complicit in fraud. At best, it's really poor judgment.