Whether a case is egregious is decided from the general factors in OFAC’s Enforcement Guidelines. The Guidelines describe it as one that “represents a particularly serious violation of the law calling for a strong enforcement response”, and give particular weight to wilfulness or recklessness and to whether the conduct was known to the company.
The label matters mostly because of the base amount it sets. A non-egregious, self-disclosed case starts at one-half of the transaction value; an egregious case that was not self-disclosed starts at the applicable statutory maximum. That is why two settlements for similar conduct can differ by orders of magnitude, and why the releases on this site state the finding in their first lines. See how penalties are decided.