Earth and Water spirits have it, too (and Guardian, and Task, and Plant as an optional power).
Don't overthink it. It's magic. Doesn't it fit, thematically, for a Beast spirit to help a Wolf Shaman run through the woods at inhuman speeds? And for a Guardian spirit to whisk a Combat Mage around a battlefield? A Water spirit to create awesome currents that rush its summoner through the water impossibly fast?
Some GMs will limit them to situations like the above, going by a "terrain it controls" interpretation. Others will just go with the more generic "it's magic" approach, will point out that spirits -- as a rule -- ignore gravity, and will let any of 'em with the Movement power fling you around where-ever you want to go...applying a modifier to your Movement rate for whatever kind of "moving" you want to do.