Back on topic - when I coached I always told my kids they need to understand the ref, as each one is slightly different in their interpretation of the laws and adjust their play to match. WB is known for carding for swearing, the players should be aware of that - especially when already on a card.
Personally, I‘m not sure I’d sanction for this specific outburst — partly because as it is described I’m not sure I’d hear it as swearing directed at me. Just because the player is looking at me doesn’t mean it isn’t just honest surprise.
However, without being on the pitch at that moment - or experiencing any other factors on the pitch prior to this incident - I have to accept that WB at that moment felt that that the swearing was both directed at him and sufficient to warrant a YC.