I wonder is it really same author with bye bye? Coz bye bye is soo green like whole forest

You won 'autorship' category for 50! Lmao
The artist writes this one themselves, while bye bye was adaptation of novel by somebody else.

Ouhhh so thats why... i dont read novel..

You don't have to. You just have to look at the title:

Author
illustrator:

I usually look up stuff via manga updates. It tells you who the artist and authors are for a particular project.

That site tells you the original source: whether it is based off a novel, a web novel, or is a Webtoon original.