HK government wanted to push forward something called "国民教育," and the materials were provided by some left-leaning organization using tax dollar without biding. That really touched the nerves of many people in HK, and people called it out as "brainwashing." With over 70 thousand/or 23 thousand people depending on who put up the number, HK government still wanted to push 国民教育 this September, starting in primary schools.

This astronauts visit was arranged by 中联办, an office set by the central government in HK, and the visit was prearranged with students from selected primary school. It was obviously a part of the brainwashing scheme as people saw it, and that triggered the protest.