Sally Hemings was never “freed”. She was not given her freedom in Jefferson’s will as were two of her sons. Martha Randolph (Jefferson’s daughter) put Sally “on her own time”, meaning she essentially retired her from working. Late in 1826 Sally was allowed to leave Monticello without being pursued. That meant that she could leave and no effort to would be made to return her to Monticello. This is how two of her daughters were allowed to leave Monticello some years earlier. Sally moved in with two of her sons, that lived near Charlottesville. She would remain there until her death in 1835
Yes, you are correct in the technical sense. However, certainly Sally being “let go” was highly unusual since the estate was in severe debt and all the other slaves were sold who were not named in the will.
https://www.monticello.org/site/house-and-gardens/sale-monticello