actually, she understand. that's why in the chapter 14 page 16 she deny so hard that she is the cause of his womanizer (which he honestly think it is the appropriate way to talk to any female) and now she count on her sister to help her fix this.
Magic 'start' from the user.
Take the fire dash example you can see the 'magic line' start next to his feet before going on to make that spiral.
So for Kunon to make water ball inside he'd have to have sent his magic power in earlier or pierce through the barrier already.
The former isn't really possible since the teacher only reveal the test after putting up his barrier.
The latter would mean clearing the test already anyway.
That said, later on
when a kid challenge Kunon to a duel and start the fight with tidal wave
Kunon casually comment "no no, you must maintain control of your magic power after release or it'll get taken over" and turn the tidal wave into bubbles.
So 'hacking' magic is a possibility, but only against unskilled opponent which the teacher clearly wouldn't be.
EDIT: Also, the fire guy's name should be Hank (the little ` is 'side way' for nn, not the more 'vertical' so)
Yes, he make it before (he even make a water cat which look and feel like the real one) but my main point is in this chapter, other than MC, no one seem to notice the fact that he also make chair which appear out of no where and also can be sitting on like normal.
It's refreshing to see a story where the author gets the balance right, the mc is incredibly talented, but not overpowered. Kunon still has to work at getting better at magic. It's strange that this kind of storytelling has become an outlier while trash like Solo Leveling is made out to be god tier.
The water mage is also a natural ladykiller... is the pun about getting women wet too crass? too blatant? it is, isn't it? yeah, gotta be. definitely. way too obvious.
...has anyone told the author yet that he's not allowed to make something like that funny? he should probably stop doing that before he gets in trouble somehow...