Sidon might- might -have assumed tiredness, but he'd already seen Link spooked by a memory that hadn't been there a moment ago, and not only had this memory obviously blindsided Link, it'd done far more than merely spook him; the young Hylian was pale and looked afraid of something.
"Are you all right?" he asked, uncertain he'd get an answer. When a brief memory had drifted back of Mipha, Link had seemed startled, but not afraid, and had confessed easily enough as to what it was at the time, even in front of Muzu, someone who'd displayed open hostility towards him. This, however, looked like something Link would be loathe to divulge. Certainly not in front of Muzu, likely not in front of Sidon's father, and possibly not even to Sidon in private.