Does anyone else have a problem being super confident when a recruiter contacts you for a job?

>Recruiter: "Hey, we're looking for someone who can do X."
>Me: "Well, I haven't worked with that technology before, but I'm sure I could do it since I worked very closely with Y."

Was I just supposed to say "Yes, definitely!" ?
If it is, then why is it so hard for me to do? I grew up thinking people would value transparency.