I think it depends on your forum settings.
I have trade muted by default but do occasionally pop in to see what’s about.
If I read a thread for a particular length of time (in trade or other category) the forum software defaults to setting me as “watching” that thread and it will show up in my main feed when updated. I have to set it to “normal” (or muted) at the bottom of the thread to reverse this.
I’m not sure if you can change the default setting that makes the forum software do this. It doesn’t bother me that much so I just do the manual setting above the odd time it does happen.
Edit: Just checked - you can change this behaviour. Go into your profile then go to settings - notifications. You can change the forum defaults regarding watching threads etc there 