This is a classic Chinese technique known as "shallow frying" and they do it with MANY of their stir fried meats as part of a two-step cooking process, to set the cornstarch "velvet" coatings, and to partially cook the meat before the final high heat stir fry. I find that I can get away with less oil, but you do want enough oil to submerge the meat. This method helps make the meat turn out tender. I made from a recipe off the internet by boiling water, brown sugar and soy sauce as "dark soy" is absolutely fantastic drizzled over the finished dish.
It's like I've lacquered it. The sweet and the heat and the spice are great.