Why is the Nintendo Entertainment System (NES) referred to as an 8-bit system, rather than a 1-byte system?
"Back in the day" computers were defined more by their word size, for example the PDP-8 had 12-bit words composed of two 6-bit "bytes". A "nibble" was half a byte, or 3 bits in this case (and here the op codes were 3 bits).

It is only in recent decades that 8-bit bytes became so prevalent as to make them the default.

Calling the NES 8-bit is less ambiguous than calling it 1 byte, keeping in mind we're talking about a system that came out in 1983.