Nothing to worry about. Wisely you seem to have made an inspection post the roof rack ride in the rain. There can be similar ingress to wheel bearings, bottom bracket and any bolt on the bike.
Marine or Lithium grease is recommended for headset races. A selection of picks can help to lift and check under bearing seals in cartridge bearings.
Any frame bolts you might remove wipe down and refresh anti seize, same for seat collar, headset top cap, stem bolts.
Water ingress can lead to surface rust on cartridge bearing outers, usually very minor and will not cause a problem.
Just programme frequent maintenance inspections for yourself which will help you to protect your bike and components.