try this formula in column E:
=IF( AND( ISNUMBER(D2), D2=G2), H2, "")
your error is the number test, ISNUMBER( ISMATCH(D2,G:G,0) )
you do check if ismatch is-a-number, (i.e. isNumber("true") or isNumber("false"), which is not!.
I hope you understand my explanation.