Amazon Timestream UNLOAD()

I am using the Timestream UNLOAD function to export data to CSV. Previously I was using the API directly via boto3. The results are that UNLOAD creates multiple CSV files with my data. The number of rows in each file appears arbitrary and unrelated to the max rows of tools such as Excel limits. Can you provide more details on how this process works; I can't find anything in the Timestream documentation? Its tedious to manually parse these into a single CSV and probably easier to use the API. Thanks for your help.