It looks like Filter>Brush Strokes>Spatter... with the minimum smoothness of '1' will do pretty much the same thing.
Okay, now that you have an image, spread by whatever means. Here's a little bonus thing you can do.
1)Use Gaussian blur on a really small radius. I used 1.1 pixels below.
2)Use that lovely spatter filter with a moderate Spray Radius and Smoothness, I used 12 and 8 below.
This makes the effect more clumpy. In the future, I'll show you how this, "Clumping," method can be useful.
Thank you for your attention. Hopefully, this will prove useful to you.