It’s entirely plausible that they’ve found some way to unlock the phone. I believe there was an article I saw just the other day that showed how to unlock an iPhone without the key code. That being said, it’s clear that the DOJ didn’t expect the backlash they’re getting from asking a tech company to bend over and give it to them. In that regard, they probably could’ve done better than to ask Apple, which has a generally positive reputation, both within the tech community and without.