The lead inspector said they were told what he was charged with and that there was a number of texts exchanged. She also clearly said specific details were not given to Sunderland by the police. Something I'm pretty sure they would not be allowed to do. It's in the BBC link quoted at the top of the page.
From the link:
"Durham Police said Margaret Byrne was told on 2 March 2015, the day of Johnson's arrest, that he had allegedly messaged and kissed the schoolgirl.
Det Insp Aelfwynn Sampson from Durham Police, the lead investigator of the case, said she met Sunderland chief executive Margaret Byrne on 2 March 2015.
She told BBC News: "They were given detail that he had met the girl and sexual activity had taken place."
How much more specific detail do they need? In any other job in the world, you'd be suspended pending the outcome of the investigation.
Edit: I'll add again, why didn't they mention this in their statement? Would Durham Police have released their statement if the full details had been in Sunderland's? It just seems like mis-step after mis-step which only makes the club look worse.