A "bin" file is likely an archive blob of some kind. Likely it is some "custom" format that encapsulates information on where the data came from or how it is to be applied to an existing installation.
If 7-zip can open it then all that means is that somewhere near the start of the file 7-zip found something resembling an archive in the data.
That it comes from Steam means it is not unsurprising that potentially at the start and end of the file might be either a program or other information that is embedded in the file that another program (Steam) might use to do something more intelligent with the file. Perhaps it needs to extract the core archive and then run commands to patch the main game files, or maybe it just needs to extract the archive blob, or maybe it needs to run installers or so on.
A .bin
file is not a "standard" archive file extension. It might contain a standard zip archive but that is by no means an absolute certainty.
If everything you need can be extracted then fine, but you do not have 100% standard archives. You have blobs that might contain an archive along with a bunch of other stuff and the error message is telling you exactly that and nothing more or less.
It is up to you to decide whether or not the message is a problem. 7-zip has no clue what you downloaded.