That applies to those who step across the border as part of a border crossing or rescue. The court decision applies it to all aliens, which is the never before applied part of GP.
Subsection (a)(1) then says that "[a]n alien present in the United States who has not been admitted or who arrives in the United States ... shall be deemed for purposes of this chapter an applicant for admission."
Who is covered by the phrase "an alien present in the United States who has not been admitted?" What else could that phrase possibly be referring to?