Achernar is talking about a specific circumstance: moving (or throwng) objects while in a sealed pressurized environment like the cabin of a space shuttle or in one of the modules of the space station. If there is air in the area, it will definitely generate resistance to movement, though the total pressure is lower than Earth at sea level.
The effect is pretty negligable is an astronaut wants to shift a 1000kg block of lead. In that case, his or her feet should be firmly braced and the movement should start out slooooow because any attempt to move a 1000kg mass quickly can result in muscle sprains and tears. Of course, however much effort you need to put in to get the object moving will have to be equalled by the amount of energy you need to make it stop. On Earth, a person can roll a 1000kg car on a level surface without too much trouble, but it takes a lot of effort to overcome intertia. This won’t change in space. The only difference is that you need to keep pushing to overcome the relatively small amount of friction between the car’s wheels and the road (and the even smaller amount between the car and the air), and when you stop pushing, the friction will gradually stop the car.
If the object has a much smaller mass, like a crumpled up ball of paper, air resistnace does become a major factor. If this ball is thrown to another astronaut, air friction will cause it to slow greatly and it will stop in mid-air if nobody catches it (if the space station is rotating, the ball will eventually “fall” against one of the walls, but that’s another story) .
A baseball raises a tantalizing question when thrown in a sealed environment. The air resistance will make it possible to throw curves but there’s no gravity to make a true sinker possible. A bigger problem is that the pitcher’s feet can’t be braced in the dirt as on Earth, so he won’t be able to do a proper windup. Plus, you’d have to have a pretty long distance, at least 50 feet, to see any effect. This is unlikely on the cramped shuttle or space station (the ball could also break something as it rebounds around the area: it will never just drop to the ground and stay there). If they ever build large pressured domes on the lunar surface, we’ll have a chance to see this in a low- if not zero-gravity environment.
Once you step out into the vaccuum of space, all air-resistance questions become moot, but inertia problems remain. An astronaut can still move a 1000kg object or throw a baseball, but now he or she is hampered by a bulky spacesuit. This factor alone will make the action more difficult than any air resistance.