There's a little more to the history.
Painter started Ronnie Johnson as a freshman and sophomore, basically letting him play his game until it was so obviously not working. Johnson left (without talking to Painter) to play for Kelvin Sampson at Houston because Painter "wouldn't let him play his game". When Painter got a commitment from highly regarded CJ Walker, Johnson publicly messaged him something to the effect that he had too much sauce to his game for Purdue. Ronnie ended up playing at Houston, and then Auburn, not averaging in double figures at either school. His scoring averages his junior and senior years at those schools were below his average his freshman year at Purdue. By the way, CJ Walker decommitted from Purdue when his dad got it into his head that he could do better than Purdue.
Irony can be a funny thing. Yeah, we should forgive, but it doesn't mean we'll forget.
I guarantee Painter hasn't forgotten, as he has repeatedly spoken about recruiting players that are a good fit. A poor fit can poison a program, even after they are gone.