The encoding used to represent the data while keying it in or burning it would have made no difference in terms of ROM space, so there's a fair point to be made somewhere underneath the "Wat". Whether your write an hexadecimal or binary number to key in a byte, in the end it's still just a byte in the ROM.

I assume the message you’re replying to was a joke...

But, while the original comment got flagged, there is a legitimate question behind the “wat” because its not at all unclear what they were referring to here, for the reasons you state.