If a stunned unit goes back to base, is it considered a move?

No, a unit returning to base due to a Recall is not considered a Move.

According to Rule 450, "A Recall is when a Permanent is relocated from anywhere to its Base without it being a Move."

This distinction is important because card effects that trigger specifically on a "Move" will not fire when a unit is recalled. As noted in FAQ 4319 and FAQ 7302, the mechanical process of a unit being sent to base after failing to conquer a battlefield (or due to other recall effects) is distinct from the Move action defined in Rule 144.