I think it’s pretty clear that the “public lands” there are referring to the sort of public lands addressed in the case. That is, those that are public by nature of their function (e.g., involving waterways).
And, I didn’t link to “Google’s version of the case”, the source is a constitutional law book that Google has scanned.
I don’t think you really need to put too much time into digging too much deeper, given that the SC has clearly upheld the federal ownership of such lands in case after case.
>>given that the SC has clearly upheld the federal ownership of such lands in case after case.<<
What other adjudication would you expect from them?