sorry I wasn't sure myself either.
best interpretation I have is....
Steve was told that when deciding whether one particular victim was more of a target than the rest of the victims, LE usually spot some signs of a different ' behaviour footprint' * by the perp.
( later on in the interview, because Steve is tired/ is grieving he says he was referring to victim not perp but I just think it was Steve mis-speaking)
* at the crime scene the perp may treat one victim differently to another, even though manner of death & weapon is the same. eg. they might return to the body again, or pose the body, treat the clothing or personal possessions differently, use knife in different ways compared to the rest of victims ( location of stabbings, how deep, the force used)
there'll be more examples but IDK off-hand what they are
edited to add:
however just because say, Kaylee or A.N. Other had more of his 'attention' during the offence I'm not convinced that necessarily means she was targeted in advance, unless LE already have other evidence ( eg this was her stalker)
You'd need to check with a psychology person on WS, but someone as sick as this might just treat one victim differently once he's inside the property. What if something is triggered in him during the attack, the way she reacts or his past issues with particulate women she might remind him of? IDK and I doubt they can be sure without other evidence