Affidavit says the DNA swab came from the "interior trunk opening" not the interior itself. It is the investigator's belief that this means she was in the trunk. The opening, defense will likely argue, is not the interior, I think.
Not saying she wasn't in the trunk. Just saying that you have to realize how this will be picked apart by any half decent defense attorney. If there was a fight/scuffle among at least three people and blood or spit flew from the blows, defense could argue that could be the reason blood or spit DNA was at the opening.
Look at pictures of the rear of a 2010 Camaro. Like most cars, the trunk door and frame are not completely flush. There is a small crack. If blood and/or spit flew during a heated fight, defense will argue that it's not unreasonable to believe some of that landed there.
I think the real problem for EA isn't that but the cleaning supplies and rags. Any DNA is there and, in my opinion, the whole car is in play as is the house, I think, at that point.
Also, in my opinion, people keep talking about how petite CM was. Okay. But, EA's injuries were said to include rib pain and a limp along with bruising of the arm and bite marks.
So, think about this - during a struggle, EA gets third party into a head lock of some sort. That opens up the possibility of an elbow to the ribs, heel stomping to the top part of the foot, as well as putting the arm close to the mouth, ripe for a bite.
Do we know whether the bite mark on his arm was measured by detectives? If so, dental records from CM could easily tell if the size matched her mouth or of someone bigger. Hopefully, detectives did this.