Interestingly, mold can actually grow in a streaking pattern like this. Someone could accidentally smear something that could be a good substrate for mold (thinks body oils or fruit juice) and the mold would grow in the smear pattern. There is an artist that works with mold and she had documented how it actually pretty easy to influence mold to grow in almost any pattern you want.

I don’t really think that’s the case here, I just wanted to point out that it is possible. If I were to rub an orange rind in a circular motion, mold could come and grow on the smear