FILTER(ALL(Dates) with External Filter Context

[JDanielHarvey]

Hoping to get some clarity about how the ALL() (aka removefilter) function behaves inside FILTER() when using a measure in a chart that should be removing external filter context be it a pivot table or a chart.
I found this formula used in a video from Sam McKay in this video where he attempts to describe what is happening as: "The max date is always going to equal to the actual date. That's why we can create this running total.". His definition of actual date show's his cursor pointing to external/evaluation context from a table in a canvas report. My understanding is the ALL() function should be removing the external filter context but that doesn't seem to be the case with the formula below used in the video I provided a link to:

30 Day Running Total =

CALCULATE( [Total Sales],

    FILTER( ALL( Dates ),

        Dates[Date] > MAX( Dates[Date] ) - 30 &&

        Dates[Date] <= MAX( Dates[Date] ) ) )

Worth noting, I have reviewed Alberto Ferrari's article on the ALL() function here. I also ran the formula through DAX Studio where the results provide 30 rows of every column in the date table from the last date in the report (12/29/2017) Sam McKay uses in the video.  

[v-yuta-msft]

@JDanielHarvey ,

---

30 Day Running Total =

CALCULATE( [Total Sales],

    FILTER( ALL( Dates ),

        Dates[Date] > MAX( Dates[Date] ) - 30 &&

        Dates[Date] <= MAX( Dates[Date] ) ) )

---

The expression seems to be correct, could you share some sample data give the expression of [Total Sales] and also share the expected result?

Regards,

Jimmy Tao