He's been hiding his Dark Matter for a while now because that was the source of everything. Tyki didn't like to show all his cards at once but despite his tease he did trust Strange. He doesn't care if he was 'good or bad' because that was something that didn't matter to him.

"It is the source of my magic," he responds to Strange in the best way he knows how or more so in a way he can understand. He's sure Strange can feel how alive it is and how much energy was just coursing naturally now that he had brought it out into the open. It was pure energy given life from his Noah.