In answer to your question, I think there are differing views on whether weed is addictive but there are two key points.
Firstly, there seems to be a consensus that it is not physically addictive in the classical sense in that there are few, if any, withdrawal symptoms on stopping (unless nicotine is being given up simultaneously) It is generally accepted, however, that there certainly can be a pyschological dependency on weed in which users become reliant on it. Secondly, the level of dependency is impacted both by the individual (their mental state etc.) and the type of weed being smoked - for example, someone with a history of mental health problems who uses skunk is more likely to develop a dependency than someone who doesn't who only smokes cannabis resin (or something low in TCH).
The situation you describe is something of a grey area. Many people who smoke dope, be it regularly or as one-offs, are absolutely fine (myself included) and treat it the same as having a glass of wine or beer. On the other hand, some people do develop dependency on it - I don't know anyone who has, but then subjective perspectives aren't always best criteria. To me, smoking for 20 minutes a night and getting 'chilled out a little' doesn't sound like a dependency any more than someone having a beer each evening to unwind but in his case, with his background and without knowing what he's smoking, maybe it is.
What I would say is that as with anything, if people are putting their vice of choice ahead of people they care about, there may be an issue but I think here, what he's using is colouring the picture. If someone had written "his mate comes round at 10.30pm every night to take him for last orders leaving me sat at home etc...." I think people would say he's being a twat, rather than he's an alcoholic. That may well be the case in this situation - that he's an insensitive twat rather than an addict.