is this included in the walkthrough?
Up to 0.12 yes, but I think this is a new chest in 0.2.
You can't miss it anymore if you're followed this flowchart so far to see all events, though.
I'm sorry, I got it following the story of 0.204[this scene will trigger after completing the 0.204 and talking to the blacksmith]
There are a few small post-game events in that version again, yes. I should have specified.
I'll have them in the flowchart again, once I publish the update to it. It's not quite ready yet, but it's close :)