All of these statements are based around very loose definition of mechanic vs mechanical engineer.

A mechanic for example can just memorize a bunch of procedures on how to service a car or a bike, and follow them. An engineer can memorize a bunch of advanced stuff like CAD and Stress analysis, and never really work with his hands.

So in this case, your statement would be correct. But both of these would just be average good, not exceptional, like SpaceX hiring makes it seem.

In general, as a mechanical engineer, your expertise is putting different materials together in certain shapes, matter states, and so on to make them do things. You may not know specifically how a bearing assembly works if you have never worked with it, but you should realize that a bearing is designed to provide rotational freedom to a part, and that mechanically, the thing that is connected to the inner part that rotates should be fully separate from the part that does not.