I cropped your image down to a small skin patch. it showed exactly 18% grey 128 RGB at 50 ire. 40-60 ire, 45ire for some setups. so, if anything, your grey card was perfect!
now to address the rest of the image. you didn’t have a screen to diffuse the sky, so it was extra bright. also the dynamic range of g7/gh4 is about 11-12 stops, but you didn’t lose too much detail in the sky. I could bring back a lot of detail. I first applied RGB curves and brought ire below 99 so lumetri wouldn’t glitch.
your hue was pretty good on the skin tone line, maybe slighter towards red about 4%, still, pretty darn close though, enough not to not have to worry about quantization image loss when post white balancing. your blacks were around 10 ire, still with those cameras not having super amazing low light, it is usually better to ETTR(expose to the right) anyway.
now, if you were trying to get a more balanced look, you could drop exposure down a third or half so that you had a little more dynamic range. maybe a circular polarizer filter(those give sky’s a bluer color and cut down a little f-stop of white light) also, blacks would be blacker and whites wouldn’t blow out so much. Still though, without a light meter, its safer to play it safe with a 18% card and get skins tones as highest priority. A little bounced light onto the actor would give the camera a little color to the skin.
All in all, I think it looks just fine. You’re way, way ahead of the curve. Trust me, I have to fix the ‘other stuff’ 😉