It doesn't have to be 2-bit. See the winner of past Black and White Jam #5, Counting Stars
The host specified that it can not have gradients and is strictly 2 colours. That game example you showed Does not have grey scale it is strictly black and white
Oh, sorry. I thought the OP was asking if they should stick to pixelated-style graphics.
no i think you're right i read what I wanted to read. Yeah you can do any art style you want just has to be strictly 2 colours