Maybe he suppressed it? Or this is just showing that Trunks is absolutely terrible at Ki sensing, leading into why him and Goten couldn't sense Piccolo laterTrunks didn't recognize Gohan's ki?
I'd love it if the reason him and Goten are so bad at sensing ki is that their "sensors" were blown out by being 5 and 6 when massive energies like Buu and SS3 Goku existed. They never got time to "grow that muscle," so to speakMaybe he suppressed it? Or this is just showing that Trunks is absolutely terrible at Ki sensing, leading into why him and Goten couldn't sense Piccolo later