Question about categorizing transactions from bank statement in EXCEL

udonlover 

=IFNA(
IFNA(
IFNA(
IFNA(
IFNA(
IFNA(
IFNA(

INDEX(Filling!$A$2:$A$11,MATCH(1,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$K2))*(Filling!$B$2:$B$11=$F2),0)),
INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$H2)),0))
),
INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$I2)),0))
),
INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$J2)),0))
),
INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$K2)),0))
),
INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$L2)),0))
),
INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$M2)),0))
),INDEX(Filling!$A$2:$A$11,MATCH(TRUE,ISNUMBER(SEARCH(Filling!$C$2:$C$11,$D2)),0)))

In the formula in the bank statement file i've adapted the ranges from e.g. Filling!$A$2:$A$200 to Filling!$A$2:$A$11 because there is only criteria up to row 11 in the Filling sheet.

In addition the INDEX and MATCH highlighted in red is now evaluated in the first step of the whole nested formula. Before it was evaluated in the last step (but only if all other INDEX and MATCH formulas returned an error).

I understand that the formula i suggested earlier works well and i'm glad it does but can't explain how it works at the moment.