He doesn't say anything to that for a moment. Not about Tess, or Riley. Not about the fact that the Capitol wilfully brought infected people into their world, and didn't bother to cure them (as far as he can tell) - just suppressed it somehow. Despite likely knowing what it is and presumably how to cure it.

And then setting those infected people loose in an arena.

He doesn't say any of that to this stranger, just shrugs and mutters, "It's all relative."