Aside from grades and AP scores, it's a lot of "showing up" dressed up as accomplishment. JV track explains itself, the debate stuff is the equivalent of getting third place in one track event at one regional meet, and Eagle Scout is impressive but IMO doesn't show anything that doing well in school doesn't already show.
Everyone applying to CMU CS or Harvey Mudd has high GPAs, high standardized test scores, and lots of 4s and 5s on AP tests. So the extra curricular stuff really does matter, because there are way fewer seats than people with good grades and test scores. And in this applicant's case, the ECs just are not there.
The applicants who are setting themselves apart via debate are consistently doing well at the best national tournaments in the most demanding and competitive formats for years; not getting 3rd place in Congressional at one regional tournament. The ones setting themselves apart with track are participating in Varsity at least a few years, doing well at State, and a likely courting at least D2 athletic scholarships. The ones who are setting themselves apart via scouting are going way beyond the minimum requirements for Eagle Scout.
Also, Northeastern and Amherst have fantastic CS programs and getting into CS programs like those at Harvey Mudd or CMU is probably harder than getting into ivies these days.