Can you all see that Aiden's plan worked to an extent? She thought it was a mistake whereas it wasn't.
So without him having to explain anything to her, she was already thinking it was a mistake. So he can easily escape from what he's just done, the consequences would most likely not befall him.
"Miss Sandra, I'm so sorry". Aiden voiced out after standing up.
Remember, he fell to the ground somehow 'cause he wanted to tap Miss Sandra's buttocks. And he didn't only tap them, he grabbed them as well.
"Do you know what you've just done?". Miss Sandra inquired of him.
"Yes, I mistakenly..." He didn't even complete the utterance.
"Where did you come from? What the hell were you doing behind me?". Miss Sandra inquired of Aiden once again.
"I was at the library, so while you were walking out of it, I was walking out as well". Aiden responded.
"You were at the library?".
..The moment Miss Sandra asked that question, her surprised expression converted to a confused one.