"I was instructed"
That was a glitch in the matrix. It wasn't that Biden misspoke, it is that the reflective mirror into which we're supposed to look as outsiders to the American political process was inadvertently revealed in a moment of unanticipated desperation.
Bush was in this same position when he was told by Rumsfeld and Cheney that there were WMDs in Iraq, the pretext for Bush's invasion. The difference is that Bush didn't lay that card on the table because he understood that it didn't matter. In the eyes of the American people, responsibility stopped with him and it was he who paid the price for it.
A key difference between Bush and Biden, however, is that Bush was a lot smarter than people gave him credit for. He asked specific questions of his advisors and was personally invested in getting it right. He may not have been the most well-spoken of presidents, but he was capable of understanding information when it was presented to him. That is why it actually took real work to get Bush to invade Iraq. He did not do so lightly.
Biden, on the other hand, has never held a foreign policy (or other political) opinion that did not meet all of these criteria:
1. Consistent with the current, relevant polling;
2. Can be articulated and understood by someone with a middle-school level education;
3. Has all and only the level of nuance of a bumper sticker platitude.
That's his record. Biden doesn't have "thoughts" and he does not have "positions." He is told what to think and say by people who make those decisions for him, because he is incapable of doing them himself. He's great at playing along with "the plan," as he is informed but is far too stupid to come up with the plan in the first place.