Actually I don't know that. When is the date on the document you quoted and the document itself so we can see the quote in context?
The legal point here is that the US Government was in default violation of the conditions which would have allowed them ownership of the property.
No they weren't. Not according to this legislation passed on December 31, 1836 - Link
Well, as that act is subsequent to the 1805 act which granted Sumter to the US, it would appear to supersede the 1805 act. This act of 1836 also contains some conditions, but I will have to read it more closely to determine if these are dispositive or not. It seems that the conditions "That all processes, civil and criminal issued under the authority of this State" applying at the Fort, might be a loophole.