It doesn't make you autistic. If that was the case, all of Tumblr would have to be diagnosed en masse. However, obsessions with certain topics to the point of dysfunction is a symptom of autism. And I don't mean dysfunction in the casual sense of "I'm neglecting my homework because I want to read more 1970s nutritional studies." I mean causing severely disruptive behaviors, like impulsive buying, monologuing, and hyperfixation. If some of your interests are intense enough to cause executive dysfunction or emotional distress, they could very well be a clinical trait. Otherwise, it's not unusual for a person to be very enthusiastic about certain interests. You seem to know when it's appropriate to bring it up in social settings, so as long as they aren't causing you any problems, I wouldn't consider it an autism trait. You're right to make a distinction based on their severity.
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I have not the kind affections of a pigeon. - Ralph Waldo Emerson