probably the same as what happened here: Forum link on iNat home page takes me to wrong thread - Bug Reports - iNaturalist Community Forum.
probably just an edge case (title begins and ends with a number). not sure if it’s worth trying to address.
EDIT: for what it’s worth, the workaround / fix would be just to add /:id to the end of the link to the forum topics, which probably would not be that difficult to do, but again, it’s an edge case. (the real fix is probably a fix to Discourse itself, in which case someone would have to report the bug over there and shepherd it through, assuming it hasn’t already been reported. if someone wanted to look into the latter option, it doesn’t have to be iNat staff to do that.)