These kind of flight essential systems go through an incredible level of code review. Including a third party review.
However, they are reviewed and tested by human beings, and human beings are ultimately fallible creatures.
This bug somehow slipped through.
They will figure out how it slipped through and rewrite their code verification procedures and make sure this mistake doesn't happen again.
They're going to be spending a lot of time convincing the Air Force and the FAA that they've fixed the flaw in the process that allowed this bug to slip through.
Thankfully this didn't result in loss of life, or even the loss of the planes.
If there were no tanker with them, I was mentally seeing them having to put down across the Bearing Straits in Russia ....