see screenshots.
COM_EASYDISCUSS_LAST_ACTIVITY_TIMELAPSE="Last activity was %1$s"
Hey Paul,
Based on what i check the code, it seems like this "Last activity was xxx" is actually referring from the question post created/modified date instead of reply time.
I also feel that is quite a little bit confuse user when it show this "Last activity was xxx", I will report this to our developer and see if we can update to a better sentence for this.
At the meantime, you can override this following language constant to another word.
COM_EASYDISCUSS_LAST_ACTIVITY_TIMELAPSE="Last activity was %1$s"
COM_EASYDISCUSS_LAST_ACTIVITY_TIMELAPSE="Thread Started %1$s"