Yes 9 bits is 2 bytes. The article confusingly says 18 bits = ~2 bytes. It is the "about 2 bytes" that is confusing. They probably mean that an extra bit won't matter too much since we are bit packing the games in a contiguous stream.
BUT
In the article they don't mean that 00000034 is a bit or a byte. It is one of the possibilities and there are 495 of them and if you index each possibly in a 2 byte integer, you can decode it back to that string and get a representation of the promotions that happened in any game.
BUT
In the article they don't mean that 00000034 is a bit or a byte. It is one of the possibilities and there are 495 of them and if you index each possibly in a 2 byte integer, you can decode it back to that string and get a representation of the promotions that happened in any game.