Kids can be categorized as "unaccompanied" if they're accompanied by an adult who is not their parent or legal guardian.
Sure. I don't think anyone was questioning that. Not relevant to your original statement about how "most" of them became unaccompanied as a result of being separated from their parents upon arriving in ICE custody though. But apparently only during Trump's term, and not Obama's. Again though, I'm not sure that's a great thing, since that suggests that a ton of kids were being sent to the US "absent parents of guardians" during the Obama administration, presumably in order to exploit a loophole in the system with all the innate risks that entails.
As bad as we might view the whole "OMG! They're separating children from parents in the immigration detention centers", I'm reasonably certain that these kids are less at risk being separated from their parents here in the US, than during the journey from whatever their starting point was to the US border. I'm reasonably certain that if we asked most parents if they'd rather their children be in US federal government custody or in the hands of "some guy I met who said he'd get them to the border cheap", it wouldn't be much of a question.
Setting that aside, there's also this issue of false/sudden drama at this. This is a pretty standard thing for law enforcement to do. Children are separated from parents and guardians in our legal system all the time. And yes, it sucks every single time. But the simple fact is that when a parent or guardian of a child is detained, we don't normally house any minors that are present with them in the same location. When parents are arrested guess where their children go? To CPS, right? They're put into a temporary facility initially, then moved into a home, unless a relative can be located quickly, and even then it can be difficult to release them once put into the system. Same basic system in place. Only here, we're dealing with kids who are also here illegally, which creates a wrinkle.
Selectively choosing to be outraged at this is silly. The same problem has existed all along. Someone (several someones) have chosen this time to make an issue of it and broadcast it to you, making you more aware of it than you were last year, or the year before that, or a decade ago, etc. It's pretty obviously politically motivated. Again, that doesn't mean that this isn't a problem, but it's a problem that didn't magically appear just now. Pretending it has is just allowing yourself to be used.
How about we discuss possible solutions without all the hysteria? Shocking concept, I know.