The official almost calls bullshit on this, but she can't actually think of any more reasonable explanation. Concealment Skills are designed to give reasonable non-question-begging results, not send up giant rocket signals of exploding absurdity.
...The official is just going to go along with what the Vice-Guildmaster said about that interesting young lady who defeated a couple of bandits and brought in five other bandits dead, alongside the bodies of two dead C-ranks. Namely: She's hiding something, she's probably not evil, and be a little nice to her if possible.
On reflection, it's probably that sword. The sword, scabbard, and belt together look much more expensive than anything else Bella is carrying.
Working admin in the Adventurer's Guild teaches you two things: One, the world is fundamentally not a normal place, and two, most of the anomalies are none of your business. If a young lady gets her hands on some kind of crazy enchanted sword and suddenly wants to visit the first floor of a dungeon, you would need to know a whole lot more about what was really going on, before you could interfere in a way that was actually helpful and didn't get your own hands burned.
"I suppose if you can move around a blade that quickly, you can handle yourself on the first floor, no deeper," says the official. "Would you like to buy a beginner's book of 『Sword』 forms for ten copper? A day or two of practice and you should be able to get 『Sword』 Lv. 1."