Sharp as anything, it's mentioning Locus' name that has Sombra's attention snapping back towards him, posture tense down to the grip she's maintaining on her gun.

Cortana.

It'd explain why his transmission got through, and why she's hearing absolutely nothing now. Locus would wait to pen them in, ensure they were thoroughly burdened— it's the closest thing to a guarantee, isn't it? Which prompts another problem: if she makes the smarter call, if she abandons York (and if he somehow survives), it'll damage her cover. All the work she's done to maintain an entirely selfless guise. Doubly so if this is a test, if they're being monitored, recorded, if—

For the same reasons she wouldn't kill Locus, she can't shoot York now. Not even for his own good.

Are you absolutely sure it's his AI talking to us.