Stealth detections have to be looked at carefully.
First, the only detections I heard about in the Gulf were F-117s, not B-2s.
If so, they may have been spotted from the side. Neither were they trying to evade the RN's radar - and indeed couldn't, because the 117 can't detect a mobile radar.
It's also possible that they had radar reflectors deployed or attached to (1) avoid traffic control problems on non-combat missions or (2) to mask the real signature from Rear-Admiral Rodney Rumbum RN and his merry crew of Nosy Parkers.
A B-2 in serious go-to-war mode is a different beast because first, it's got wideband all-aspect LO (this is why, like the freshmen down at Yale, it has no tail) and second, it has some ability to detect the radar and warn the crew.