Scientist is a word which has had its meaning stretched way beyond the likes of Einstein and Newton and the Curies. Those were actual scientists. Most papers that are called studies are graduate students’ term papers. They should say that in the articles. They say scientists and they mean graduate students.
As to the origins of helium in the Earth below the ground: a Geiger counter is a device that detects alpha particles emitting from radioactive materials. Each pop represents a single alpha particle detected. Not nearly all particles get detected. When it makes the crackling noise it means a lot of alpha particles. Alpha particles were the first evidence of what is called radioactivity.
Another name for alpha particle is helium nucleus. A uranium atom decaying to a lighter isotope gives off alpha particles, gamma rays and heat. Consider the amount of uranium that must be found in the core of the earth and you will have a pretty good idea where all the helium is coming from. Any other theory is at the very least worth considering but is probably more of a conjecture worthy of someone who is high on marijuana.
That is the first thing I thought of but they were careful to mention they were using Helium 3. Helium 4 is what an alpha particle is.