Walking isn't a sign of intelligence. Starfish walk, using hundreds to thousands of feet uder each arm, and sometimes the arms themselves. Sea pigs also walk, and neither have a brain.

Besides, you're strawmanning their definition;

performing a task indistinguishable from a human

is very different from

can perform a complex task that is indistinguishable from the work of a human

A good calculator can compute arithmetic better than a mathematician, but it cannot even parse the work of a high school student. Wolfram Alpha on the other hand gets pretty close.

A wind up toy can propel itself using as few as one appendage, but fails at actually traversing anything. Some machines with more legs can amble across some terrain, but are still beaten by a headless chicken. Meaningful travel needs a much more complex system of object avoidance and leg positioning, which smells more like AI.

The way AI is often used isn't "do a task that a human has done", but "replace the need for a human, or at least a specialist human". Chess AI replaces the need for a second player, as do most game AIs. AI assistants replace much of the need for, well, assistants and underwriters. Auto-pilots replace the need for constantly engaged pilots, allowing bathroom breaks and rest.

Meanwhile, you can't use a calculator without already knowing how to math, and even GPS guided tractors need a human to set up the route. These things aren't intelligent in any way; they're incapable of changing behavior to fit different situations, and can't deploy themselves.