I assume that James is using "sat/kw", to refer to "satoshi per kiloweightunit" as a means to express the fee rate of a transaction. "Weight" here refers to what replaced "blocksize" as a blockspace limit in the protocol rules with the segwit softfork.

I'm seeing "sat/kw" for the first time in this context. I've seen wu used before to refer to weightunits instead of w, and "virtual bytes vB" seem to be more common generally.

I've explained the relationship of blocksize, virtual size and weight in depth here: Is there a difference between bytes and virtual bytes (vbytes)?