If she says she'll explain later, then Strange trusts her to explain later. He nods, realizes that Shura might not see it, then starts talking.

"Understood. My house is nearby," Strange explains, as he watches Shura. "You can stay there until whatever this is passes."

Because he's still not entirely sure what this is. Having spent most of his life in cities, Strange's knowledge of murderous plants is next to nothing. But what he knows is that it's made Shura tense and Shura being tense and acting odd is making Strange tense in return. He continues to pet Shishi as Alistair continues to hide behind Strange's legs.