DAX CONTAINS and CONTAINSROW

I have a question re the diffference between the two , in the following boht return true or false

EVALUATE
ADDCOLUMNS (
    Table1,
    "N", CALCULATE ( CONTAINS ( Table1, Table1[Customer], "Tom" ) ),
    "M", CONTAINSROW ( {"Tom" }, Table1[Customer] )
)

But when the above are used for measures, Containsrow needs to be re written;

CONTAINSROW( VALUES( Table1[Customer]), "Tom")
or
CONTAINSROW( {"Tom"},IF( HASONEVALUE( Table1[Customer]),VALUES(Table1[Customer])) )

but if used inside a measure it can use the same order as the calculated column, such as ;

CALCULATE( [TotalUnits], KEEPFILTERS( CONTAINSROW( {"Tom"}, Table1[Customer] )  ))

Containsrow can be used as it was for a calculated column, could someone explain or point me in direction of some information
on how this is calculated, not MS Docs.
Ive attached the above examples.

Richard.