There are some things to consider. Maybe the votes were fair and based on the films' quality:
1) the 2nd year's film may have been written better, but the 3rd year's film VFX seem to be top quality, cinema-level possibly complete with motion detectors and CGI, and that's very impactful and impressive as it is, regardless of the script's quality.
2) 2nd yr's film is more lowkey and emotionally sensitive. Like what you said, boys are more likely to gravitate towards the flashy, action packed, sci-fi film over romance (Boy's Love at that).
On the other hand, since this is Asian culture, it's possible the third year's film automatically has the upperhand because it's their last film before they graduate. The juniors and student body look up to their senior and especially look up to Kikuchihara. Kikuchihara already acts well, but I don't think it's impossible to assume majority are biased towards the 3rd year's alien film because they're attached to the seniors and feel like they deserve to win the contest before they graduate. Like a farewell gift to them or something. It's not interschool contest anyway, so the gravity of the result isn't that big. But it's not a completely unfair win if the 3rd years are as good everyone claims and their film is like Guardians of the Galaxy and Avengers level of picture quality, CGI, and VFX.
Bro you analyzed this better than I did props to that!
Your question made me think LMAO
Wait so how did the third years win? Seems like 2nd years was written better. OHH J GOT IT, it’s an all boys school so they damn would’ve like the aliens more