OK, elaboration follows: ;-)
The instrument your Ham friend used looks like a somewhat upscale NanoVNA, good device for this application.
The three traces of the 2nd plot look like impedance, resistance, reactance.
Impedance is the vector sum of the reactance(not good) and resistance(good).
This is the basic info from which VSWR is calculated. This resistance BTW is not ohmic resistance but rather the effect of RF power radiated to or from the antenna. (Antennas are completely reciprocal.)
The lower trace in the 2nd plot I believe, is the reactance and from what I see it is capacitive (-ohms) across the band, so increasing the series capacitance will tend to reduce that reactance and drop the VSWR a tad. Sounds backward, I know, but increasing the amount of series capacitance will lower the cap reactance. Antenna length is also in there, so 2 variables.
The glass composite wingtip when installed will cause some dielectric loading of the antenna which may tend to lower the tuning a bit. I wonder if some one has already measured for any significant effect? In any case, your numbers are good to go. Any improvement from your less than 2.0 VSWR would be hard to detect.