I didn't look at that tool, but just reading this suggests that you're being shaped/policed more aggressively on egress (in the direction of your provider) than you are on ingress. Shaping and policing (typically) both use the same mechanisms as interface buffers to temporarily store packets in order to prevent congestion/discards. The distinction between them is that shaping actively buffers packets, where policing will more aggressively drop them (and aim to trigger a TCP congestion event) - in most cases, policing will involve a burst bucket that is somewhat similar to a shallow queue.

This would make sense if you have a higher bit rate from your provider for down vs up.

What speed connection do you have, and what speed connection did that tool report?

If your connection is fast enough that that tool is unable to max it out for whatever reason (say you're on a poor WiFi connection), you will experience no bufferbloat.