OP, at this point I'd contact the gunsmith and ask exactly what was replaced, since your not sure.
Yes, they were probably in the frame, but, since your not sure, you need to rule them out. Only parts in the frame to replace for lightening the trigger without touching the slide would be the TRS and hammer spring. If he happened to put even just a spring kit in to truly lighten the pull, that would also include FP spring and FP block spring, which means slide work.
I'm not doubting you, (I'm doubting your GS) but as I said, you need to know what was done. IMHO, to "significantly smooth and reduce the trigger", would mean that more than the TRS or HS were replaced.
Regardless, you need to know what was done to your pistol before contacting CZ. It may have voided your warranty. If so, call CGW. They'll get you the parts you need.
If GS is ruled out, contact CZ customer service. They'll take care of you and send you a shipping label.
Once you do get it taken care of, please post back. This is very odd indeed.