All the packages are physically downloaded in the .julia/packages folder, regardless of the environment you added them in.
When you activate . you tell julia to create a new environment in the current folder (pwd()) by creating a Project.toml and Manifest.toml file an save them in the same current folder. This file contains a list of the packages you added in this new environment, but physically they all reside in .julia/packages (even if you added multiple versions of the same package in different environments).
More info here:
https://julialang.github.io/Pkg.jl/v1/getting-started/