They must have reasoned that entering them in octal or binary means more digits which means more space.

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.