Antenna Tuning for Source Impedance not equal to 50 Ohm
This is a setup I found on the Nordic semiconductor dev website:

Impedance matching with source impedance different from 50 Ohms
This is the situation you have. You have an output from a PA, a section of a transmission line (eg. 50 Ohms), and your antenna. You want that the impedance looking from either end of the TL to be 50 Ohms (in a 50 Ohms system). That is why there is another matching network right at the output of the PA, in addition to the one right next to the antenna. Think of this extra matching network as an extension to the output of the PA such that you think of this as its output.
Now the matching network close the PA also serves the purpose of filtering harmonics, which could be an issue when passing regulatory certifications. That is in addition to matching.
Your antenna tuning setup is Ok. Just make sure you calibrate your VNA right at the point where the antenna's matching network starts.