Why my root.hcl configuration works if find_in_parent_folders() function suppose to find from bottom to top, but instead it actually looking for files in child folders?

root.hcl:

locals {
    account_vars = read_terragrunt_config(find_in_parent_folders("account.hcl"))
    region_vars  = read_terragrunt_config(find_in_parent_folders("region.hcl"))
    env_vars     = read_terragrunt_config(find_in_parent_folders("env.hcl"))
}

And the project structure:

    ├── demo
│   ├── account.hcl
│   └── us-east-1
│       ├── dev
│       │   ├── env.hcl
│       │   └── vpc
│       │       └── terragrunt.hcl
│       └── region.hcl
└── root.hcl

How does it work in such way?
My suspicion that it works in a way how include works in C++. When I run terragrunt apply from the bottom of some folders, it goes upward and simply copy-paste a content of config inside itself. But I didn’t find any proves of it.