During WatchOS 10 dev betas and now into 11 dev betas, I am still seeing were stands are not being detected. What I do not know is if the steps are detected. But here is the situation.
Today: I was going on some wiring outside and in the basement. I was clearly up and moving around for over an hour. I can see on my camera's I went outside at 15:50, came back in at 16:18. Then went to my basement and was working down there from 16:19 until 16:30. After that cleaned up my mess. So I was up and down stairs and without a doubt standing. At 16:50 I got the reminder to stand.
Other cases: 1: I get home from work about XX:10 . I have to walk about 50 ft from my garage to my house, up stairs, take the dog out, make dinner, and finally get my chair to eat and at XX:50 I get the reminder.
2: I'm at work, I'm going to get lunch and I have to walk pretty far and again at XX:50 I get the reminder. This is very rare, but it has happened.
Now, in a odd twist. I get up in the morning at XX:50, I have 10 steps to the bathroom, and I manage to get that hourly stand.