Yes, pinching is a type of topping. It's safer to pinch than to cut through the main stem, which can expose the vascular tissue of the plant to pathogens, not a great idea for an already-stressed plant such as one in the process of re-vegging and adapting to a new environment. Just pinch the very terminal bit of leaf bud, where the soft new growth is coming out, and be sure to pinch just below the thickening that is the base of the new leaves.