No, a lot of people have forum threads set to show the most active in the past 2 weeks (or another short space of time) so even if a thread is 6 months old (or more) if someone replies to it, they can see that it has been replied to. And 3 days really doesn't make it that inactive :-)
You can set your Forum options by going to the "My Home" link at the top, scroll down and click on 'Edit' next to the words "Display preferences, number of shown threads, languages, colors...".
Have fun!
Regards,