It's broken. I believe it was due to a recent page that allowed for the detection of art mediums (pencil, marker, etc), but it messed up tag detection for the regular ones.
For the artist detection, it's because artists have been for some time now able to change their pixiv username (thing that appears after /stacc/ or in their shortlink, pixiv.me/blablabla). This was never accounted for because pixiv usernames were assumed to be static for a long time, but they're just about as easily changeable as twitter handles. Someone might've tweeted about it and others got on board to change their handles, perhaps to better line up with their names on Pawoo/Twitter.