No, /8 is not the same as the topic. /8 points to the 8th post and the timestamp corresponds to that of the 8th post.
If you compare the ?page=2 variant to the actual post it links to then you will get the same timestamps.
For instance:
wget -q -O - https://meta.discourse.org/t/topic-list-previews-legacy/101646/959|grep published_ti
<meta property="article:published_time" content="2020-05-09T04:29:46+00:00" />
wget -q -O - https://meta.discourse.org/t/topic-list-previews-legacy/101646/?page=2|grep published_ti
<meta property="article:published_time" content="2020-05-09T04:29:46+00:00" />
Looks like it: Incorrect or failing oneboxes for links to other discourse instances - #14 by techAPJ