If anything, they are like banana flower buds - which I originally mistook them for - until @Presunto pointed that out to me. Slightly fruity but without a distinct taste, maybe because the dish we had here was sautéd with dried shrimps, which would’ve altered its own flavor profile. I enjoyed the dish more for its textures: delicate, almost like asparagus.
Not distinctly tart like lily buds.
Those are boiled cassava leaves, called daun singkong in Indonesian. Traditionalists would have a bit of the cassava leaves, together with rice and other meats, in each mouthful as they eat nasi Padang with their hands.
This short clip by a visiting Indonesian tourist showed her eating, Indonesian-style, at Restoran Pusako.