A lot had changed in the times they were from. Buffy would have a long time to catch Dawn up. "I'm not sure Xander that's here knows...so please don't drop that bomb on him." he was already recovering from the spell of pink kryptonite, he didn't need that sort of thing either.
When they walked past the creepy guys again, she did shoot a glare in their direction, a silent message to back the hell off, before looking ahead again, keeping her eyes open. "Depends." she said with a shrug. "There's only one species of demon, so you never really have to know the hundreds of kinds at home. But they possess people, so there's humans trapped in their bodies with demons using them. Which means we can't kill them. We have to trap and exorcise them, which is a whole new set of skills." she said with a shrug.
"You'll learn more about the details as you go. But the basics are, those seals I mentioned? Think of them like locks. There's a demon named Lilith going around and opening the locks. When she opens enough, Lucifer walks free." scowling, Buffy crossed her arms over her chest, then looked over at Dawn. "Like, the Lucifer." which was hard to believe, since the guy didn't seem to exist in their world.
Which Buffy was more than okay with, they had enough big bads trying to end the world without some fallen angel stepping in and making things harder.