Thanks for the query to H.C.M. Forum.
In my opinion your partner may have hemoptysis
( blood from lung cavity).
2nd reason may be hematemesis
(blood from stomach due to acute gastritis
or esophageal varices
May be due to injury of internal part of cheeks due to cramps.
In my opinion physical examination may find exact cause.
X ray chest will reveal something.
Consultation with a physician is very important.