they clearly said rebellious phase like you would said to teenager. and the MC is trying to distance himself with the family.
regardless if you can differentiate between tantrum and rebellious pahse, or differentiate between furstation (in tantrum) and depression (in rebellious phase), the characters treat it as rebellious and consider it soemhtiing a kid would do by the author which is weird, unless theres translation mistake and they actually said tantrum
I think you're confusing Western "rebellious phase" = Puberty, with the "rebellious phase" in a japanese Conformist context.
Teenagers aren't
allowed to rebel... They're already expected to have "Common Sense". And the entire school system is designed to drill that into them. On pain of Pain.
The only age kids can "rebel" is in the 4-5 yr age range, where kids aren't yet taken seriously and they can still act out to a certain extent.
This is the whole premise of "
Shin-Chan" ** , where a 5yr old can comment on the Adult World and do things against "Common Sense" and Convention. And can get away with criticising it. Because he's only 5. So it's heavily leveraged for social criticism you can't ordinarily express in Japan.
*
Note the demographic on that one... In Japan that one is intended for an *adult audience...
In the West it's aired as a Kid's Cartoon, because "it's about a 5yr old kid, so it's for kids, right?"...