"Oh, I'm certain he would," Strange idly responds, with a little shrug. "He's always eager to use his—"

And then Strange cuts himself off. Because wait a fucking minute, he knows what 9S would do if Lambert were involved.

"You know, if you want to truly test your hacking, you'll have to practice on different people. The more you practice on someone, the more likely it is that they'll figure out your tricks and discover a resistance."

Strange is basically saying 'if you're bringing Lambert into the picture, go torment someone else who's not me.'