[A portal opened up in the Arcane world, sucking all the Arcane people, where did they get taken to? The MHA universe!]

The Arcane characters sucked into the Mha world and that's where the portal opened right onto the field where 1A was training. Yet they were sprayed.

Izuku: Who are you? Are you a villain?!

Aizawa: Stand down!

Bakugou: You heard him!