What Causes Light Bleeding While Engaging In Non-penetrative Sex?

Hello! Tonight, after being fingered by my boyfriend, there was a small amount of blood. It wasn`t thick or dark. It was quite light and...diluted? This occured one time before about a year ago so it is not a common thing. I haven`t had sex, or engaged in any sexual activity other than with my current boyfriend so I don`t think it can be anything too serious. I read somewhere that when a girl is fingered more deeply it can cause light bleeding due to the new pressure, however, I don`t quite understand this concept. I was hoping you could shed some light on this situation and ease my nerves a little! Also, I don`t know if it makes any difference but he also used two fingers to go deeply which he doesn`t usually do. Thankyou in advance for taking the time to reply!