Bud Powell shells — the bebop left hand at tempo: a two-note voicing (root + 7th, or root + 3rd a tenth up) struck on beat 1 and held, then once more on the swung "and" of 3 pushing into beat 4. That is all the left hand does at 200+; the right hand plays the line. The shells here walk a ii–V–I–VI in C (Dm7 D–C, G7 G–B, Cmaj7 C–B, A7 A–C#), the bass walks quarter notes, and the kit keeps the standard swing ride.
The difference from swing-lh-shells is placement: Levine's version (fig. 21-4) anticipates each chord by a half beat; Powell's default is on the downbeat, with the push coming later in the bar — on the "and" of 3 — so the bar line is stated, not leaned into.
Listen for the shell as punctuation rather than comping: one "thunk" on 1, one on the push, silence otherwise. Practice: metronome on 2 and 4, shells only, held note really held; then move the second hit to the "and" of 2 or drop it and hear how the time still works.