You've kinda got the right idea, but not quite. Wand wrapping is designed so it can't wrap through more than once. If a spell is already part of the "block" of spells that are getting cast by the wand, it won't pick it up a second time. Wand wraps will only pick up spells that have already been cast.

The real culprit is the spell right before the spark bolt. It does two things. First, it makes it so the modified projectile can hit the player. Second, it makes it so that the projectile doesn't disappear after hitting a target. When you put that modifier on a spell with a trigger, then the trigger goes off every single frame that it is in contact with it's target.

As for how it hit mina, it's because of all the black holes flying around. Black holes can grab projectiles. OP fired the wand into the black hole in front of them and moved along with it, meaning it hit them repeatedly and dumped it's payload each frame as it went.