Hiccups are paroxysmal, involuntary contractions of the diaphragm
that occur along with contractions of the larynx and closure of the glottis, arresting the inflow of air.
Anything that causes irritation of and compression around the diaphragm can cause hiccups.
You friend's theory about eating too fast (and may I add, too much) can indeed be one of the causes. But since your hiccups are not necessarily precipitated by eating, you should know that without any other symptoms, the culprits usually are unconsciously breathing in too much air at once, rapid swallowing (again unconsciously) or stress.
Stop worrying. (And stop scanning the internet for diseases!)