If a kitchen (new build) only has one reset GFI does that mean there is only one kitchen 20 amp circuit?
Not necessarily. The only way to verify this is to attempt to trip the other outlets.
Some may be on a different circuit and may not trip. If you attempt to trip outlets near the sink area and the GFCI (with the buttons) does not trip, then you have another circuit or they may be outlets that are not properly located on the load side of the GFCI.
There should be 2 GFCIs, one each for the 2 required 20a small appliance circuits. One might be in the pantry, breakfast nook or dining area if there is counter space there. You might also have a GFCI in the panel serving one.