If a complaint was filed, the police have to investigate. Clearly, the woman's attorney tried to extort a settlement by threatening a police investigation and Dak called his bluff by counter suing. The lawyer had no choice but to file a complaint.
I don't know the venue where this alleged rape occurred but a parking lot does not seem very private and Dak was an NFL QB so the possibility of a witness seeing them in the car, getting in the car, or getting out of the car would be likely, or would it? Dak admits having been with her consensually, but now she has to prove it wasn't, or get a grand jury to believe it wasn't at least. In a civil suit the burden of proof is much easier. A mere preponderance of evidence as opposed to beyond reasonable doubt. But preponderance does not mean no proof at all.
I suspect we will soon hear about a witness, possibly a friend of the woman claiming she was told of the rape around the time it occurred. The woman's lawyer seems like the type wo will "find" a witness like that.