Both string.getByte () and Hex.decodeHex (string.toCharaArray ()) are processes that convert a string string to byte  type, but there are some differences.
string.getByte() Converts an ordinary character string to byte  type. The byte length after conversion is twice the byte length when converted with hex.
Hex.decodeHex(string.toCharaArray()) Converts a character string with double quotes added to a hexadecimal number (in short, a string type but the content data is a hexadecimal number) to a byte type.
Then, what happens if the character string to be converted is a hexadecimal number such as "1" or "a", an ordinary character, or a character string that is seemingly indistinguishable?
As a result, different byte  type strings are generated for each.