I think the real distinction is between "experienced" and "expert". Anyone can become experienced by keeping a large collection or large variety of animals, but experience doesn't always (and often doesn't) equal knowledgeable or competent. There are a good number of people with large collections that are little better than novices, and likewise many with smaller collections that could easily be considered intermediate to expert keepers.

Simply put, when it comes to being an expert (in any field), it's all about having a substantial store of knowledge, and having enough experience to understand and discern when it's applicable.