The way bring your own data works, means that the AI doesn't know how many movies it has in it's database, so it can't tell you. When you use bring your own data the process to query it looks like this:
- You enter your question in the UI
- Your data is searched for relevant answers to the questions you have asked
- The results of the search are sent to the AI, along with your question and it provides an answer based on this data only
So the AI only has access to data that was retrieved from your data store, that is relevant to the question "how many movies do you have in your knowledge based". The actual search that occurs is just looking for data relevant to this in you data, it is not counting your items. The AI is probably getting 5 relevant pieces of data back, and so that is what it knows about.