Americans or British sometimes don't use grammar well. Some particular places include:
--Text messages on phones
--Postings in social media
--When speaking aloud, especially in informal situations.
You are right. These are all correct:
"The government deported a foreign tourist." (Active voice)
"A foreign tourist was deported by the government." (Passive voice).
"A foreign tourist was deported." (Passive voice, so we don't need to say who did it).
"The government deported some foreign tourists."
"Some foreign tourists were deported by the government."
"Some foreign tourists were deported."
A complete, correct sentence would be "American volunteers were deported from Lombok Island."
Headlines often leave out words, abbreviate, use initialisms, or various slang-like words to shorten the headline. This headline is not a complete, correct sentence. It is acceptable as a headline.