ALL with Table vs ALL with Column

I have a question related to how ALL works when I pass in the Table vs when I pass in the Column. I understand it removes any filter applied to table or column. I noticed that If I use it with COUNTX and pass the column (COUNTX(ALL(columnA)), columnA) it would count only the distinct values (why?), and when I pass the table (COUNTX(ALL(tableA)), columnA) it would count all values. Is this behavior by design?

I do not understand how this relates to removing the filters.

TIA