As a bit of an after thought, do you have a moisture filter on your compressor ? If a bead of water made it's way through it would cause that. I still do things like that every so often fella, it's the trouble airbrushing at higher pressures with a non absorbant surface that you can't correct mistakes on.
Shell looks good though, you should be pleased with that
That patio and and moss pit board effect looks photo real what technique did you use to get them so good ?
