If it was blood and it was coming from his stomach (from a bleeding ulcer, for instance), then it will have looked like coffee grounds
. Blood in the stomach coagulates when it mixes with stomach acid.
If, on the other hand, it looked bright red and wet, it would not be coming from his stomach. It could, however, be coming from his esophagus. A severe enough case of GERD (acid reflux) can cause a raw and bleeding esophagus.
In either case, your boyfriend should not be drinking alcohol at all.