I think I know what you are thinking of.
The problem is--we don't know which swab/location of sample she is referring to when she is talking about presumptive but not confirmed semen when you are then asking if it could be saliva.
There were a lot of swabs taken--of the girls bodies AND the clothing on Abby and the clothing in the water.
If the comment is referring to on Libby's body, it likely would have first been identified by an alternate light source (which we know they used from testimony on like day 2). If something lit up that wasn't detectable by the human eye, they are going to assume in order of likelihood 1) semen 2) saliva 3)sweat. And depending on what light they used, they can get an idea of what to test first: polilight (blood and semen), wood’s lamp, Bluemaxx, and UV light (saliva)
https://www.sciencedirect.com/science/article/abs/pii/S2468170920300357
Then they would have moved on to presumptive testing (there are some newer tests that let you test for both blood and semen at the same time) to try to narrow it down and then confirmative testing.
On the other hand, if that comment is referring to swabs taken of the underwear in the water:
Delphi Murders trial: Day 9 live blog
"On the pair of underwear found in the creek, she tells the jury there was no blood or seminal fluid found. Bozinovski told the jury that she took swabs from the crotch area. Those swabs showed Abby’s DNA. The tells the jury the underwear were stained, but not by blood."
So, if they do the acid phosphatase presumptive testing on the crotch of the underwear and it comes up positive, the problem is that:
"
Other body fluids can contain other forms of acid phosphatases that may give a false positive reaction
such as vaginal fluid (
vaginal acid phosphatase is elevated in prepubescent females)."
We explore the examination of exhibits for scientists to recover evidence of human contact to uncover DNA evidence from physical touching and bodily fluids.
www.forensic-access.co.uk
So they would then do a consumptive test--which would definitively rule out semen.
I haven't seen any account of the DNA expert testimony from today where she mentions the presence of saliva--but the news media would tend to focus on the blood and semen aspect so is it a matter of they didn't put it in their reports or the expert didn't say anything about it. I'm sure that once we get to see accounts of the cross examining by the defense, we'll know if saliva was present or not because they will certainly ask about it if it was not specifically mentioned as being ruled out.