In the Dim Sum place I usually go to (in the U.S), they call the pan-fried bun stuffed with Chinese chive and shrimp 韭菜馅饼. I came from Northern China and the shape and size of that bun are, by any standard, 包子 rather than 馅饼. I wonder if this is normal in Cantonese or just that restaurant. If it's normal, is the distinction between 包子 and 馅饼 cooking method (pan-fried vs. steamed) rather than shape and size?
Yeah. 包 (usually sans 子, most of the time, or sometimes as 包仔, and sometimes as 鮑[仔]) is a steamed bun, whereas 餡餅 is baked/pan-fried.