It's not, because that's not how drafting works. Now if you mean that they were picking Primo no matter what because they fell in love with his character and didn't stop to consider that Sengun was actually a better player, I can see that. But that's still them thinking Primo was better and picking him for that reason. They certainly didn't JUST scout one player over the past year. They scouted all over the board, especially when it became clear they'd make the lottery and thus could end up with a top-four pick. Also, Sengun being available wasn't "changing cir stances". The dude went at 16, not 13. Likely the Spurs thought just like the other 12 teams that passed on him that he had flaws that made him not BPA.
It's possible (but not reasonable to assume) that the Spurs are uniquely incompetent now and passed on players like Haliburton and Sengun because they can't deal with a guy falling. It's more likely that they just agreed with those other teams though. In this case, they could be wrong, like they appear to have been about Haliburton. If that's the case, though, they're most likely wrong because of how they set up their board, not that they forgot how to use their board in the critical moment.