It is clear in the movie that every child is allowed to have a guardian.
Liu Peiqiang's wife was terminally ill and gave up treatment. This guardian is Han Ziang by default, and Liu Peiqiang himself is an astronaut arranged by the state to carry out the space station plan, which does not conflict with the lottery.
In addition, in fact, as an orphan of Han Duoduo, it is possible to fight for another guardian quota, but Liu Peiqiang and Han Ziang did not do so, and the quota of this dungeon was virtually given to another person. From this perspective, Liu Peiqiang and Han Ziang are actually very selfless people.