Apparently many of the fans actually knew that Spike was going to be in Angel Season 5... BEFORE he died on Buffy.
I think most of us probably already knew that Spike was going to show up on Angel before this Season 5 premiere... so the credits may not have spoiled too many people. The marketing of TV shows is never very concerned with preserving spoilers: they just want to get people to watch.
With today's reactors, however, it's really fun to see them surprised by his appearance at the end of this episode.
UTU49
2020-11-18 23:58:13 +0000 UTC
The second scene after the credits is a single, 3 minute, 45 second shot introducing all the main characters in their new setting. According to Whedon's DVD commentary, it took 27 takes to get this one long shot because "inevitably one actor is always going to have trouble with their lines, and it's usually going to be the one who's at the end of the take, because that's just my fate," - Wikipedia