ACT English Practice Problem

I ride this trail nearly every day (- not on a bike,) but on “Luigi”.
(The parenthesis above means underlined).

F. No change
G. day; not on a bike
H. day not on a bike
J. day, not on a boke

I would’ve expected there to be no comma since “on ‘Luigi’” is not a independent clause. However, the answer key says that the answer is F? Can anyone clarify? Thank you.