Yes, and in addition to that & the 1st floor having a separate entrance that is not viewable from the back of the house (if that is where he may have watched the house from, where there is an uphill parking area & woods which is a somewhat concealed vantagepoint in an otherwise populated neighborhood), the 2 people living on the 1st floor were younger and "lower classmen" (Freshman IIRC), and so did not have the same longevity or closeness of friendships as the older students living upstairs who were "upper classmen", so they may not have really been part of the same group of the 4 of them that were targeted. JMO
So if X, M & K were not only close enough to eachother to choose to live together in the same house, 2 of them also worked together (X & M), and 1 of their bf's (X's bf E) was a member of a nearby fraternity, and all 3 women were in sororities, 2 of them together in the same sorority (X&M), they seem like they were a tight "gang of 4" who had a lot in common and spent alot of time together. IIRC, the 1st floor housemates were new to the sororities they joined in the Fall of 2022 and were "little sisters" of X, M & K, so didn't necessarily travel in the same circles as the 4 of them on a regular basis. JMO
So if the killer stalked and/or was focused on the 4 of them who spent a lot of time together and were very close, it would be another reason why he didn't care about going after the 2 living on the 1st floor and they were "spared". JMO