It looks like FolderBrowserDialog inherits from CommonDialog, while OpenFileDialog inherits from FileDialog, which in turn inherits from CommonDialog, so I would say no, FolderBrowserDialog is not a customization of OpenFileDialog. They are unrelated.
MSDN documentation for OpenFileDialog states:
"If you want to give the user the ability to select a folder instead of a file, use FolderBrowserDialog instead."