When you're looking for superheroes, like Ladybug for example, you tend to seek out the places in need of some saving. Which is how Alya wound up near the building that had seemingly exploded. She certainly isn't expecting to see anyone familiar there, especially not Adrien Agreste.

"Adrien, you too?" Who is kidnapping her classmates? Who'll show up next, Marinette? Kim? Ugh, Chloé? "Not too long ago, I've just been wandering. Do you know where we are?"