Since it looks like a num, Qlik assumes that's what it is. If you want to ensure it's treated as text with the 0 in front, you could use the text() function when loading your fields:
CODE_T: LOAD text(CODE) AS CODE, Rank FROM [C:\Users\QLIK\TEST_DATA.xlsx](ooxml, embedded labels, table is CODE_T) where Rank = 1;
VALUE_T: LOAD text(CODE) AS CODE, DESC, VAL FROM [C:\Users\QLIK\TEST_DATA.xlsx](ooxml, embedded labels, table is VALUE_T) where Exists (CODE) ;