One thing that I love about this series, is that despite remembering and being involved with her past, Maria is still fundamentally a girl. Her past is a huge part of her, but it doesn't overwhelm who she was reborn as.
Because he's not supposed to be there, he's supposed to be in his office, so he snuck out hiding his identity.
Also because the Manga is doing a few stories out of order here. In the novel he's also hiding his identity because things are still awkward between him and Maria for that whole "trying to rape her in his office" thing. The manga put in a few later stories that have them acting more friendly, though, so the hiding from Maria bit doesn't make sense here. In the novel Maria absolutely would not have let Lloyd come along if she knew who he was.