But you're skipping the most important part of 1802(a)(1), which is subparagraph (A), *not* subparagraph (B). Here:
1802(a)(1) . . . the Attorney General certifies in writing under oath that —See it? The surveillance must be directed at communications that are transmitted by specific means (i.e., communications means which are used exclusively between or among foreign powers, as defined). Or, the surveillance must be directed at technical intelligence from specific property or premises (i.e., property or premises under the open and exclusive control of a foreign power, as defined).(A) the electronic surveillance is solely directed at—(i) the acquisition of the contents of communications transmitted by means of communications used exclusively between or among foreign powers, as defined in section 1801(a)(1), (2), or (3) of this title; or(ii) the acquisition of technical intelligence, other than the spoken communications of individuals, from property or premises under the open and exclusive control of a foreign power, as defined in section 1801 (a)(1), (2), or (3) of this title;
Importantly, note that there's nothing there regarding agents of foreign powers. It's about foreign powers, period.
More importantly, what you're misunderstanding is the definition of foreign power. For the purposes of 1802(a), a foreign power is as defined in 1801(a)(1-3). Foreign powers as defined in 1801(a)(4-6) are not relevant to 1802(a). Notice that you quoted one of the non-relevant definitions, 1801(a)(4).
1802 doesn't include terrorists of 1801(a)(4) either.
But hey, if people want to argue that the surveillance is within the four corners of FISA, who am I to pop their bubble? The lawers are dealing with it, the administration is putting out their legal arguments, and lame arguments on FR don't carry any weight except educational.