Altium Via stitching vs Via Shielding
Via shielding is meant to shield a net (read: a track) from disturbances: Think of an RF signal trace that gets shielding GND vias left and right of it that follow the trace.

Via stitching is meant to connect a signal on one layer with the same signal on another layer. Think of connecting a VCC polygon pour on top with a corresponding power plane. The vias generated for this kind of connection are meant to be evenly distributed over an area (which can be along a line, but doesn't have to be)

Both work similar but via shielding follows a trace without you having to specify the area manually.
Since both add vias of a requested net, you can accomplish similar tasks with them. Its more like a different use case in mind.