Your question is slightly ambiguous.
Could they have been genuinely ignorant?
with the connotation of that they should have known?
"should have known" implies that they might not have actually known, but we refuse to accept genuine ignorance as an excuse.
In this case, because genuine ignorance is still on the table, neglect(ful)/reckless(ness) best covers your scenario. The former refers to an active decision to not engage, the latter to a lack of care/awareness to even consider it.
I would favor referring to neglect when the person didn't do something they should have; and recklessness with the person did do something they shouldn't have.
...or was their alleged ignorance disingenuous?
As if someone were to close their eyes and drive into traffic, and then defend their actions in the event of a crash because they didn't know any cars were there.
That is not the same scenario. Here, genuine ignorance is off the table. They knew they were driving into an intersection, they knew they'd be held accountable for seeing other cars on the intersection, and they then wilfully acted in a way that evaded blame for the problematic behavior while knowingly and willfully still continuing the problematic behavior.
When genuine ignorance is off the table, and you are stating that you know for a fact that they had the necessary awareness at the time; then you're talking about willful ignorance/neglect/recklessness ("willful" being the key phrase here).
The distinction between willful ignorance, neglect and recklessness hinges on the part of the problematic behavior you want to focus on.
- If your primary concern is that they're lying to you about what they knew, then it's willful ignorance.
- If your primary concern is that they knowingly didn't do something, then it's willful neglect.
- If your primary concern is that they knowingly did something, it's willful recklessness.
This distinction is very contextual and it's not clear from your question which part you're trying to stress.
Legal terminology
I feel like it may literally be a law term.
All of the provided terms have some kind of legal connotation, but I'm wondering if you're thinking of "consciousness of guilt"?
This refers to evidence that the person knew what they were doing and took specific actions to make themselves look innocent, actions which a genuinely oblivious person would not have taken. The existence of the unusual actions implies (and can be argued to prove) the existence of their awareness beforehand.
Closing your eyes as you enter an intersection is such an example. A person who ends up causing an unexpected accident would not close their eyes in order to cross an intersection, but a person who wants to evade blame would pre-emptively close their eyes so that they could be technically correct when they argue that they "did not see the other car".
The act of closing their eyes (or even just the claim that they did so) reasonably proves that they were aware that being on the lookout for other cars was their responsibility, but then acted in a way to try and avoid that responsibility.