Because if you were an Organization spy, ya would because I wouldn't tell ya absolutely anything without confirmation ya were really Haibara.

And you're not pryin' enough to be tryin' to do that, so either ya realize I'm useless and would try, or yer really Haibara.

But it's good to get confirmation.

...or is it you don't ahve to worry as you've got Gin's car key as a trophy at them being taken down?