This lab result disagrees with the view that humans are like machines. While a machine can be programmed to reproduce out consistent results given an output with little or no margin of error, a human is subjected to inconsistency, as shown in the differing reaction times. Human factors like mood, dexterity and concentration however play a role in determining how well we can improve or achieve consistent results. A person who concentrates really hard on catching the ruler each time has a much higher chance of getting a more consistent result than a moody person who just goes through the motion of the experiment. However, that will never be able to match up to the results produced by a machine because they possess the computational power and precision that humans lack.
A second notable difference between humans and machines is the ability to improve and learn with practice. Results using both right hand and left hand improved over a few trials generally even though are some fluctuations.
I agree with your reasoning that machines produce more consistent and stable results, while humans cannot produce consistency especially since they are influenced by their moods, environments, and other possible distractions. Since machines do not think like humans do, their minds are one-sided and once told to do something, they perform that task with precision. Therefore I follow the same belief that humans are not like machines.