Law enforcement sources tell us it was actually Ronnie's girlfriend, Saffire Matos, who called the police that night ... after they'd gotten into some type of argument that allegedly got physical. We're told when officers arrived, they spoke to both parties, and determined Ronnie was the aggressor.

As for why ... our sources tell us officers observed visible marks on Saffire's body which they determined she sustained during the alleged fight. We're told that was one of multiple observations that spurred police to slap the cuffs on Ronnie.

This is interesting because it shows Saffire had enough of a problem with whatever was going on to actually pick up the phone and dial 9-1-1. Since Ronnie's arrest, she tried to downplay the alleged violence.

She posted a statement in the aftermath, telling her followers not to believe media accounts of what had happened, insisting she and Ronnie were "fine."

Ronnie's attorney, Scott Leemon, tells us, "We are still investigating the incident of last week and have not yet received any of the police reports. Therefore, we will continue not to comment while our investigation is still ongoing. As we have all learned in the past, initial reports can be and are often incorrect.”

Of course, as we reported, this is bad news for Ronnie ... who's been down this road before with his ex, Jenn Harley. He ended up getting probation in that DV case -- and a judge could deem this latest arrest a violation of that probation.

Speaking of Jenn ... she drove all the way from Vegas to come get her and Ronnie's daughter, once she heard he'd been arrested.