Grimrock

I just found out how to cast spells with none spellcasters. I found a sword that could cast fireballs. To use it, I had to give my rogue 1 point in concentration. After that he was able to use a caster ORB that also needed conceantration 1. Once the Rogue wear the orb and you click on it he does not slash (that would be normal), the rune Windows opens So of course I gave him another point in fire magic and suddenly I got a rogue caster. I am sure this works with all classes.

That's no bug. It is intended that every class can learn all skills as long as they have spare points to assign. So when somebody wants to train his Minotaur Barbarian magic he can do so.

If you read the mage and battle mage descriptions, one of the perks is that they can cast magic from bare hand.
Any other class can cast as long as they have a staff or orb that allows it.

Even the "hands-free casting" perk of those two classes (wizard and battlemage) is really only relevant at the beginning of the game when you don't have any casting tools. Past that point, you'll be using those tools for the relevant bonuses and extra options they provide, no matter the class. The wizard also benefits from having a much larger innate energy pool than anyone else will get with equivalent Willpower.