The guy at the end is the royal magician, and is also the one who sent that bird to Kaid's job last time.
He basically came to tell Carol to get off Kaid because of many reasons.
1. There's been 0 proof of her actual work, even the boss monkey they supposedly defeated was finish off by Kaid.
2. A LOT of other ladies who's been aiming to be Kaid's partner, all with higher ranks, wouldn't stay quiet on this.
So he gave her a challenge, that is to capture him within 3 days.
Well, she basically made herself super sticky glue, that also will send out poisonous smoke if the mage try to burn it.
He escaped from that, but then she used her other skill to spread out basically a mace spray++.
This improved version is specialized such that even the mage's own healing spell couldn't cure him of it and required Carol to give him her medicine to deal with it.
So in the end he is salty but a win is a win for her.
But with that said, the issue of her being E rank still remains (she can't party up with Kaid for quest, seeing as people would just say Kaid is lying about her work to give her the achievements)
And Carol decide she'll take an exam that'll prove her real skill.