Light raised his eyebrows, surprised at the explanation, though not as much as he probably should have been. A year ago, maybe the mention of aliens and rifts in time and space would have made him roll his eyes. But the Death Note and Shinigami had shown him a world he previously hadn't known existed. And of course, he himself had wound up in the past.
Hearing that she had a coworker with her confirmed Light's assumption that L could show up with him. It was definitely better to lay low, if that was the case.
"That's fascinating," he replied. "My story isn't nearly as exciting." He had prepared it in advance, a mix of truth and fiction, to get close enough to what had happened without needing to explain too many details. "I went into my room to grab something. When I got there, I couldn't remember what it was - you know how that happens sometimes. I was just going to leave, when all of a sudden, I remembered and turned to get it, but once I had fully turned around, I was here." In truth, once he had gained all his memories back from the Death Note, he was in New York, but the story was close enough.