Blame nicotine.
Hiccups are actually fairly common among smokers and tobacco users. They're a result of swallowing nicotine.
Hiccups are most common among those who use chewing tobacco, snus, dissolvable tobacco tablets. They swallow tobacco juice and hiccups can result. They are not common among pipe and cigar smokers, who neither swallow nor inhale smoke, or users of nasal snuff.
If you tend to "gulp" your vapor (or used to do the same with tobacco smoke you inhaled), then you're sending part of the inhalation to your stomach, part to your lungs. The stomach part produces hiccups from the nicotine you put there.
No big deal. Stop the gulping of vapor and see if the hiccups don't stop.
That "gulping" of inhaled vapor/smoke/whatever can also cause burping, as you've forced air to your stomach. That air has got to go somewhere. Up, down ...