It’s a bit hard to translate into English, I think. The first word, 冬眠, combines 冬 (winter) and 眠 (sleep). So, “winter sleep” is what we call “hibernation” (noun) in English. Being a noun, the verb form is created by appending する, creating 冬眠する. And this refers to any animal that sleeps during the winter (hibernation).
冬ごもり combines 冬 (winter) and こもり (to shut oneself in (e.g. one’s room); to be confined in; to seclude oneself; to hide away). As far as I can tell, this refers only (mostly?) to bears. (This Weblio page doesn’t specify bears, but it does say 冬ごもり is different from 冬眠, and close to sleep.)
So, I read it (not direct translation) as “Precisely, bear hibernation.”
While looking for something more definite, I found this Japanese blog post which says (with as best I can translate):
My first thought was “maybe it’s because bears don’t really hibernate.”
Turns out my very limited bear metabolism knowledge is out of date. Maybe the comic’s is too. Up until fairly recently, scientists said bears didn’t truly hibernate because their temperature didn’t drop low enough. The terms seemed to be “torpor,” “deep sleep” or “winter denning.” But it has been discovered that there are a huge amount of metabolic changes in bears during winter, so they’ve changed the definition of hibernation to be more than just “sleeping; core temperature drops.” 30 years ago, AFAICT. https://bear.org/do-black-bears-hibernate/
The “staying indoors during winter” part of 冬ごもり seems to be a match for winter denning. Newer editions will have to remove the aside on the panel, to keep up to date with current bear science.
I think this 「"いい人"で終わっちゃう」 as the type who when he confesses his feelings to a girl, he “ends up being a ‘nice guy’”. As in, “You’re a nice guy, but I don’t feel the same way about you.” Similar to “I like you as a friend” in English.
I know that 「どうでもいい 事」 is a thing not worth bothering about, so I imagine 「どうでもいい人」 is a person not worth bothering about, in this case meaning someone that a woman isn’t going to fall in love with.
I could be wrong on any of those points, but that brings me to:
First Panda: “He’s the type who ends up being a ‘nice guy’.”
Second Panda: “Ah, a ‘nice guy’ no one cares about?”
First Panda: “To put it bluntly.”
And this was all right after Panda suggested that Handa-san’s a nice guy.
