For the same case, what specific type of bony defect is this?

Most vertical periodontal osseous defects are not a single, uniform wall pattern along their entire depth — they commonly present as combined defects, transitioning between different numbers of bony walls (e.g., 1, 2, or 3 walls) at different depths/levels of the same defect, which is the most common real-world presentation of a deep, narrow infrabony defect like the one described.