I think you're on the right track with this. The issue, apparently, for Spielberg is the definition of a movie. From the article it seems that his definition includes the requirement that a film must be shown in theaters to be a movie. I don't think the average person thinks of movies that way. Especially not in today's world with Redbox and streaming services.

Personally, I never really thought about the definition right now, but I think a crude definition would include something regarding runtimes since I think part of what defines a movie is its length. You can do more with additional time than a 30 or 60 minute TV episode can do. However, you can do more with a miniseries or episodic TV over the long term with regards to character development, story arcs, etc. I think the definition of a movie has to be somewhere between the individual episode and the miniseries.