Sherlock accepts the sandwich but doesn't eat it, setting it aside. He is particular about food, so it could just be that he doesn't feel like eating right now. But there's more to it too. He's even more guarded emotionally than Watson, even if it's hard to tell because he becomes rude and acerbic instead of going silent and still, but Ted knows him now, better than anyone save for Watson, and he can probably notice that Sherlock is grieving as well. With his partner and friend, yes, but also for a woman that he knew well and liked, as well as for the loss of his own mother so long ago.