Total Downloads is the combined sum of MP3 Downloads and HLS Downloads.
If you previously saw a single "Downloads" number in your analytics, that metric only counted MP3 downloads. Total Downloads now gives you the complete picture of your audience across both traditional MP3 delivery and HLS streaming delivery.
Your underlying data has not changed. The previous "Downloads" metric is now labeled "MP3 Downloads" (same data, clearer label), and HLS Downloads is a new metric available to series in the ART19 Video Beta.
See also: Understanding Video Analytics and HLS Metrics · Why did the metric labels in my analytics change?