That is a good question, sumbodhi.
Such effects require at least a “focused mind.” The more concentrated or focused the mind is, it gets easier for such phenomena to materialize.
This is why faith or saddha (a genuine belief) in whatever one is thinking about matters.
The person who reported this experiment is likely to have had a real determination to see the effect. Therefore, his/her javana power would be intense.
– On the other hand, one who does not believe in such an effect may conduct the same experiment, and his/her GOAL is to show that it is a foolish idea. So, they do not “put a real effort” into their thoughts while doing the experiment.
We can confirm this by thinking about our own experiences. Think about two different cases. In one, we really want to get something done. In the other, we just want to get something done because a parent is asking to do it and we had no choice.
– In the first case, we are enthusiastic and our minds work at “full potential.” In the latter, we just “go through the motions” without any real effort.
Of course, someone who can get into jhana samapatti (Ariya or anariya) would have “more javana power” in their thoughts (citta). In a jhana samapatti, citta with the “same focus” or “arammana” can flow uninterrupted. Thus the “intention” is fully focused.
– That is why such yogis can even do “supernormal” things, like making a flower with their mind power.
– An analogy, in this case, is comparing an oil lamp to a laser beam. An oil lamp just put out a little light. In a laser beam, light energy concentrated. It can cut a metal sheet. The mind power of an average person (even when focused) is like that of the oil lamp. That of one in a jhana samapatti is like a laser beam.