It is, a tool of his trade really, and one he knows his brother uses. As much as they ignore their emotions, they are there, and it's what he is after here.

At the silence he waits, pouring the water teapot as he does so, letting it steep. "All of it."

No it was a lie, but it was enough for him to put it all together, along with the argument. It told him what had happened as surely as if John had. Sherlock must know that by now.