"Magic" in some definitions is any phenomenon that can't be rationally explained, identified, or recreated by the use of scientific method. Princess Bubblegum in Adventure time said it best; "All magic is science! You just don't know what you're doing, so you call it magic!". On the other side really, really, really advanced supper-science can also be described as "magic" if all its laws and principles are beyond you ability to reason or understand them. As such they can replicate the appearance and effects associated with magic through a mechanical means.. Like that gun (Caster) in Outlaw Star. My theory is Gaius had and was using a "Caster" or something like it... Everything else was prestidigitation.
