The article you linked to does not say that the Griffiths claims caffeine dependence is "purely psychological" in the sense that you appear to be using it as an

The article you linked to does not say that the Griffiths claims caffeine dependence is "purely psychological" in the sense that you appear to be using it as an opposite of physical dependence. The article states that Griffiths thinks that caffeine dependence should be considered a psychological disorder, like other substance addictions. If you look at the sources the Wikipedia articles cites for its mentions of Griffiths, the National Geographic article compares caffeine addiction to heroin addiction and attributes to Griffiths a claim that as little as half a cup of coffee a day can produce physical dependence. The paper appears to agree, from the information in the abstract.