Google Maps are intentionally offset in China to comply with regulations because the global version doesn't have a license to operate in China: https://en.wikipedia.org/wiki/Google_Maps#Google_Maps_in_Chi...

Apple Maps in China uses Autonavi maps which are licensed by the Chinese government. Note that these maps are different than the maps seen in Apple Maps outside of Mainland China.

Google and Facebook weren't blocked using your Hong Kong sim because roaming sims tunnel data out of the country and connect to the internet there (like a vpn!).