Thinking about it: in certain markets, the HSDPA speeds are not that good: averaging 1 Mb/s. So if you're speed drops half that, you may think you are not throttled.
I had experienced this before: Once I did not know I was throttled for 10 days. My speed was OK since I was in a market with bad H+ speeds. The market had good LTE coverage but I had a non-LTE phone. When I called later, my data for that month was at 9 GB. I was surprised because I was able to do regular things. The technician informed me that my account was indeed throttled.
So speeds are in the eye of the beholder.