I've had the same thing happen and its probably due to overenthusiastic masturbation that stretched the skin a little too much and caused tiny tears. Due to the bunched nature of the foreskin this is difficult to observe unless you notice that the areas where the scabs were is smooth while the rest of the skin shows striations.

Just lay off for a while if you can, or use vaseline while masturbating to enhance the stretchability of the foreskin.