Does the mfr provide a "how we measure it" document?
Test fixturing, sample circuits, etc. are important.
You'll see this kind of thing with devices designed for use in embedded systems - For instance, there are a lot of "monolithic WiFi" antennas, which are designed for 2.45 GHz, but only on a specific board layout in a specific environment. It's a tiny SMT "chip" with no connector, and if you put it into a SMT clip fixture, it probably doesn't read 50 ohm resonance.
If your measurements are showing more inductive, it might be that the mfr is assuming some capacitance to surroundings in the circuit. I notice in the picture that there's a bunch of capacitors and spots for capactiors. It might be that the mfr intends for you to add components for a specific application.
