I think Windhorst is twisting DeRozan's words trying to read between them. DeMar never says the Spurs were engaged in an S&T. He says he and Lebron talked it out and agreed on it. My guess is that the Spurs and DeRozan likely did talk about S&T possibility as part of "extension" talks (which were legal until the moratorium even though re-signing talks are not). He knew the Spurs would be willing to deal him if they could get back a good deal, and so his agent solicited offers. He got the general idea that LAL wanted DeRozan, but when that fell through, he started gauging Chicago's interest. None of that is illegal either. Clearly based on everything reported, there wasn't any handshake agreement in place between the Spurs and Bulls before the moratorium, and the Westbrook trade makes it pretty obvious there wasn't one with LAL either.
Windhorst is just trying to drum up controversy by acting like it's the same thing, but without even knowing whom the Spurs would have wanted the Lakers to draft with their first, there's little proof. Unlike Washington (or eventually Indiana), the Spurs were never going to be able to make that pick directly, so they would have had to tell LAL whom they wanted. The Spurs didn't seem to covet anyone in that range enough to get a pick some other way, and given how cheaply those picks were being sold for, they definitely could have gotten one. Of course, you could stir the pot and say that they wanted Primo with that pick and just pulled a Masai and overdrafted him once they knew they didn't have the later pick, but there's too much evidence against that too.