Paddling.com defines primary stability as how steady a boat feels at rest on flat water, and secondary stability as how stable it is when leaned on edge, usually in rougher water.
Wide, flat-bottomed recreational boats are strong on the first. REI puts the tradeoff simply: wider hulls offer more initial stability, while narrower hulls can go faster. A narrower touring boat can feel nervous the moment you sit in it, then hold its edge well in waves.
So "tippy" sometimes means "unfamiliar." Paddling.com even suggests a serious beginner consider a boat with better secondary stability and grow into it.