This patient had facial trauma so he could have swollowed his own blood from the inside of his mouth. I have found that patients that swallow their own blood do not like it to sit in there stomach for too long so the body does what comes naturally and rejects it (vomits). This is from my own experience as I have been to a fair bit of facial trauma. As well blood mixed with alcohol can also give the apperance of there being more ingested than there actually was. There are many reasons but I find this to be the most common.