The connotation of "Dashboard" is that it may give you a trendline, but not necessarily be able to pull up trendlines for arbitrary time intervals.
There are of course dashboards that do so, but it is reasonable to argue that those are really dashboard/reporting hybrids.
It sounds like TFA is referring to a dashboard that is fully featured in that department. Few are, even these days.
In any case, if the product doesn't make autodefinition of intervals and side-by-side comparisons as easy for managers as pulling up two PDFs side-by-side from their email or (if they are old school) printouts, then there's a deficiency compared to the traditional reporting solution, despite any advantages in other areas. And, if a dashboard-oriented product cannot present a nice list of autopopulated intervals, then either you need to go the report route, or instead of making reports you'll find yourself logging in every morning to manually create those intervals for the front row.
Also depending on the nature of the data, reports can sometimes be used as supporting documents in legal/business procedings, and so must be presentable in a the form of a document.
Finally when your data gets large enough to become cumersom. the report model starts to make sense in that it schedules DB resources.