She was for a moment startled by his reaction before she recalled. Of course he wouldn't know yet. She'd had to explain to Lily, after all, so why would she have thought Dean would know any different? "It's ... complicated," she said. Since Severus was here, she didn't honestly want to get too much into it, and his motivations were entirely kept to herself. She hadn't even told Lily, because ... well, awkward. Then again, since Harry had announced it all to the entire hall ... well, anyone who showed up here after the battle was going to know.
She sincerely hoped they all kept their traps shut as well, but it wasn't as though she could control them if they weren't inclined to. "But he was never a Death Eater. Not truly. He was working as a spy for Dumbledore the entire time. From the moment he signed on as a professor up until the very end. He helped Harry, as much as he could without ... bringing down suspicion on himself. No one knew, not until after ... after the battle," Ginny said evasively. "Even Harry didn't know until close to the end." She thought that was as good an explanation as she could give while still retaining most of the details.
Lapsing into silence, she walked along with her hands in her pockets, her mind drifting back to the battle. To all the pain, the horror, the chaos of it all. The revelations and the recoveries.