Unity : apk vs aab for the same scene

I’m new to Unity , i use mac os catalina , unity 2019.4 and build for android/mobile.

I downloaded a unity project from internet. It’s already in format of unity project. so i just copy it into my unity folder. THere’s only 1 scene there. I can load , run and built with no problem. It created 160mb of .APK file. But now i need to bring this project into my other project (let’s name it B project ). Basically i only need to bring that single scene (and all its linked assets) into that B project. What is the proper way to do this ?

Last time, what i did was: i export the whole things as package then imported it into my B project. When i open the scene , i can run and build with no problem. But it create .AAB rather than .APK and size is 300mb (2x of the previous APK). Is this big size become the reason it become AAB ?

Can someone tell me what’s wrong ? why the size is doubled when i just build the same scene. Does unity build includes unused asset ? because in B project there’s already asset from my other scenes. What is the proper way to do this ?