In addition to the sensor size variation possibility, remember that actual back-focus distance will affect FOV, and assembly tolerances may even mean a slightly different FOV from one camera to the next within a model line. I wouldn't be surprised if a manufacturer may measure the FOV on a number of finished cameras and then pick the numbers that are most favorable for the marketing.
Slightly related example: back when I was working in car audio, it was common practice (probably still is) for amplifier manufacturers to measure amp output at maximum supply voltage, and use that as their power ratings. Since an automotive electrical system regularly varies between 12V and 15V (with dips and spikes well outside that range), you'd get substantially more measured output power when providing the rails with 25% higher voltage, which looks much better on the ad copy... but also means you get significantly lower output when running on battery (engine off) or at *normal* operating voltages of 13.5-14V.
At that time especially (early 90s) the "wattage race" was similar to the "megapixel race" with everyone trying to come up with some new trick or edge to have better numbers than the other guy, which as often as not with cheaper models included conveniently omitting (or small-printing) specs like THD (total harmonic distortion), which is a product of signal clipping caused by pushing the output past the rail voltage - gives you a lot more measured RMS output, but sounds like crap; this might be considered analogous to low-light or low-noise specs on high-MP cameras.
Since there was (and AFAIK still is) no industry-standard way to specify output, let alone any regulatory controls, there was no way to really know how accurate or meaningful those numbers were. The high-quality, "professional grade" amps used regulated power supplies, meaning they would give the same output across the entire output voltage range, so if you were buying a 200W amp, you knew it would give you 200W all the time (these were usually very up-front about THD and other related numbers as well).
But I digress...