'Otaku' is really one of those words western journalism and fandom have sort of watered down in their loaning of it. An 'Otaku' is a Hell of a lot more involved then "buys a few cheapo trinkets." If you're memorizing facts about a train or insect and recite them to another as well as cross-reference information when giving an oral opinion you're pretty much an 'Otaku'--or rather, that is indicative of such. It's a state of obsession.
While looking for examples of an Otaku bedroom to serve as a physical representation of the above paragraph I stumbled upon this article on CNN. Run on sentence. Here is a paragraph from said article I think is worth keeping in mind.
I think this is important to keep in mind, especially considering Miyazaki's comments. Miyazaki is criticizing an unspecific number of individuals for being Otaku despite these animators being infamously poor and restricted to spending months at the studio without ever going home, if you're a director."Though it is true that some people might have hobbies that keep them at home, I don’t think interest in media or commodities means that you aren’t interested in people. People who consider otaku losers without ever meeting or talking to those who identify or are identified that way are probably just reacting to negative stereotypes. Or they are discriminating against hobbies that they do not share or understand."