I believe you are correct there. If software has no explicit licence, either on the binaries or the source, then the copyright owner could prevent you from using or distributing that software. If code doesn't have a licence then you should either request permission for your use of it from the copyright holder, or just don't use it.
The fact that someone makes their work available to look at doesn't give you the right to use it, copy it, modify it, or base new code on it.
https://choosealicense.com/no-permission/Quote:
For users
If you find software that doesn’t have a license, that generally means you have no permission from the creators of the software to use, modify, or share the software. Although a code host such as GitHub may allow you to view and fork the code, this does not imply that you are permitted to use, modify, or share the software for any purpose.
Your options:
Ask the maintainers nicely to add a license. Unless the software includes strong indications to the contrary, lack of a license is probably an oversight. If the software is hosted on a site like GitHub, open an issue requesting a license and include a link to this site. If you’re bold and it’s fairly obvious what license is most appropriate, open a pull request to add a license – see “suggest this license” in the sidebar of the page for each license on this site (e.g., MIT).
Don’t use the software. Find or create an alternative that is under an open source license.
Negotiate a private license. Bring your lawyer.