Titles are often clickbait. That's why it's good to read the article:
"Usually, visitors are free to take pictures at air shows, but the U.S. military prohibited citizens of certain countries, including China and Taiwan, from entering the Osan Air Power Days event due to a recent series of illegal filming of Korean military facilities by Chinese people.
But the suspects violated the ban and secretly entered the air show venue to commit the illegal act."
The article also says " The police are currently reviewing whether to apply for an arrest warrant for them, the agency added. ".
So for now they are not even charged with anything. This is just badly written, clickbait article. It's not even clear if they broke the law by filming anything or just entering the air show while being Taiwanese. For all we know they were just escorted out after someone checked their documents and the author invented everything else.
That's what I meant. It's not like they sneaked into closed airbase. They bought tickets or just entered with everyone else. The problem was there is specific law forbidding Taiwanese citizens from attending. They are not charged with anything.