Just review the fact of the cases.
In the McCollough case, there was no question that a drunken intruder "mistook" Tank's apartment for his own and then got belligerent when ask to leave. The legal point of contention was where the actual altercation happened-- at the apartment door entrance or away from the apartment near a flight of stairs, In the former case, McCollough was defending himself and in the later case he would have been assaulting the interloper who was trying to leave the premises. That was the point of legal dispute. McCollough had a plausible defense that he was the actual victim and that the accuser was lying about where things escalated. I am a bit surprised that there was a plea deal, given the circumstances, but we don't know everything about the case. But, the University's presumption of innocence until proven guilty made sense here.
In Ruby's case, she was the clear and undisputed aggressor who broke down two locked doors and chased after the person who allegedly took her phone. She has to justify why she committed the felonious act and yes, she still gets the innocent until proven guilt presumption but there is a preponderance of evidence against her and she has acknowledged engaging in breaking down doors to "get back her property" (which like it or not. does not provide a legal justification for aggravated assault). I know, for the hundredth time, you believe with heart and soul that Ruby was totaly justified and that she should be given a medal of honor but that is not how the law works. If you can accept that your feelings about the situation are not the same as the legal statutes for aggravated assault, you might just be able to comprehend the differences.
Seriously, what more do you need explained to understand that these situations present two very different legal situations and why it is impossible for the University to back Ruby for again breaking down to two locked doors and smashing a mirror in the bedroom where the accuser had fled for safety.