Crocodile

Quite possibly because when the H1N1 first was recorded in Hong Kong, the Hong Kong government found it necessary to quarantine almost 300 people in a hotel room, even though most had not come into any contact with the person that had the virus. They were quarantined for 7 days without any possibility of leaving or valid reason for their detention.

Also, then the government was hunting down anyone with suspected virus and hospitalising them or putting them into a quarantine area outside the city.

So, while the question may seem a bit strange, it is not totally unreasonable.
To the OP: Your information is a little incorrect. Traditionally, the winter is not the peak flu season in HK. Worrying about being "detained" is no way to start a holiday. Your holiday is not for many months and alot can happen by that time. Relax, make sure you have travel insurance and enjoy.