It's becoming more common to see footnotes in adverts like that in general.
As an example, Discogs.com [0] explictly states the states where you can remote from. "This is a remote position. Open to candidates located in OR, WA, CA, CO, ID, AZ, TX, IL"
In this case, the employer incurs cost in every state they create a nexus, and so yes, there is a limitation. My company uses a PEO that is able to employ people in every state, so we don't have this limitation, but the cost to carry an employee varies a lot from state to state... and that is before considering difference in local pay rates.
As an example, Discogs.com [0] explictly states the states where you can remote from. "This is a remote position. Open to candidates located in OR, WA, CA, CO, ID, AZ, TX, IL"
[0] https://discogsinc.bamboohr.com/careers/118