I don't think this dashboard is a legacy dashboard. It is a fairly new dashboard, created as a dashboard view within a notebook. It is only affiliated with that notebook and can only be accessed through that notebook or a workflow of that notebook. 

Accessing it within the notebook: Click View; There is a Dashboards section at bottom of View, and it is in there.

Accessing it within the workflow: Click on the job run; Top right of output has a dropdown menu with the options "Code", "Results Only", or "Dashboard: <name of dashboard>"; I choose Dashboard and I can see it, then I click Export as HTML and I get a file that starts downloading.

From the link you added, if this were a legacy dashboard, then I should have the option "Clone to Lakeview Dashboard", and I do not.