They are obligated to arrest one of the parties if there is an admission to arguing and/or getting physical. Probable cause for a DV charge can be as simple as yelling, swearing, slamming a door, standing in front of someone, or stopping them from hitting you. Literally. Almost 70% of DV charges get dropped in the US. Look it up. I worked in this field for years, buddeh. I know how it works. I've seen many different scenarios. It is fucking ridiculous. Very fucking ridiculous. It's a fucking joke, but that's how it works.
There was an admission of physical contact, and there was physical evidence of it. They were obligated to make an arrest. If they deemed her as the aggressor and were going to arrest her, Chuck had to say something that constitutes probable cause for them to arrest him instead. It's literally that simple. I don't have personal experience in CA, but I have over 7 years experience in the field. Do you? I looked up the California laws, and they're almost identical to the state I worked in, as they are in almost every state. Cali typically has harsher laws and typically requires less probable cause for an arrest to occur. They have broader classifications for the sole purpose of being able to arrest people with less reason.
If Chuck, his wife, and whoever called said that there was no physical contact and they weren't fighting, they would have no probable cause and wouldn't be obligated to make an arrest without a witness testimony. That obviously wasn't the case. "Bruises and lacerations" is probable cause. If Chuck said he was standing in her way or restraining her, and she said she was scared of him, that is probable cause to arrest and charge Chuck. For fuck's sake you kids are either just straight retarded or incredibly stubborn. How many times does a simple concept need to be explained to you in order for you to comprehend it. You don't have any experience or knowledge in this field. I do. What would be the purpose of me lying to you about it? You can actually just fucking google how it works and see for yourself.