Hopefully that's all it was, certainly this will help. If it doesn't you may want to consider replacing the sunroof seal. I found water in my X5 in multiple locations after a torrential downpour. The seal was the culprit, simply allowing too much water into the vehicle which the drains ultimately couldn't keep up with. The profile of the seal is a "D" shape and over time it squeezes down and loses it's spring force. Cheap part but pain in the ass to change as you have to remove the pano glass. For me I had the entire headliner and interior pulled so that I could dry it out and seal it up properly.

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Current stable: 2005 LMB X5 4.8is, 2000 LMB M5, 2004 JB M3 6spd coupe