That’s an approximate rule of thumb. The definition of a newton is the force required to accelerate 1 kg by 1 m/s². The ocean level gravity of earth just happens to be around 9.82 ≈ 10 m/s², thus a 100g weight feels approx 1N of gravitational force.

And redirecting you attention on to the “offsets” scam too.

Ever wonder why climate change is such a problem if 1.5 pence per liter petroleum burnt can undo the damage? Spoiler: it can’t. You can’t sequester CO² for that cheap, and CO² isn’t the only issue. “Offsets” are not certified by any trustworthy third party, and companies intentionally don’t pry too much, so they can say “Oh sorry, didn’t know” if anyone investigates and discovers they did squat-all.