Unknown Genre assigned to Videos

Cannot recall seeing this issue reported - apologies if already done:
I store my Home Movies in a separate shared folder (ie. separate from my copies of commercial movies) and do not have "Retrieve Descriptive Metadata" ticked for that shared folder. This ensures that these videos do inadvertently get assigned the wrong metadata (I use on-line metadata for my other shared folders) and therefore do not appear in the library under categories that require metadata eg. "Movies", "Series", "Directors", etc.
They do however appear under the category "Genres", under the genre "Unknown". Is this by design or is it a bug? Given that there shouldn't be any metadata collected for these files, I was surprised to see them there. If by design, is there any way to assign all files in a folder and its subfolders to a more meaningful Genre (eg. "Home Movies").
I store my Home Movies in a separate shared folder (ie. separate from my copies of commercial movies) and do not have "Retrieve Descriptive Metadata" ticked for that shared folder. This ensures that these videos do inadvertently get assigned the wrong metadata (I use on-line metadata for my other shared folders) and therefore do not appear in the library under categories that require metadata eg. "Movies", "Series", "Directors", etc.
They do however appear under the category "Genres", under the genre "Unknown". Is this by design or is it a bug? Given that there shouldn't be any metadata collected for these files, I was surprised to see them there. If by design, is there any way to assign all files in a folder and its subfolders to a more meaningful Genre (eg. "Home Movies").