That is semantics. As a developer, I understand why you are technically correct.
As a user, it doesn’t make any sense to see “Last post: yesterday”, click that to see the last post, and see that the actual last post is from months ago. Why would a user who can’t see a deleted post care that there was a deleted post? That partially defeats the point of having the post deleted.
Imagine Gmail doing that to your inbox every time it automatically deletes spam:
Hey @Mittineague, new mail! Last one is from 1 second ago!*
* (Might be spam tho! ;))