openstreetmap - Understanding the difference between coordinates projection in OSM and Google Maps in China

I'm looking at the coordinate differences between Google Maps and OSM. I'm a noob in the technicality behind GIS.

Having read:

1. 
   

   EPSG 3857 or 4326 for GoogleMaps, OpenStreetMap and Leaflet

   
   


2. 
   

   How to adjust the difference between the coordinate from OpenStreetMap and Google Maps

   
   

I'm not sure whether is it because of #1 or #2 that causes the difference for the same coordinate that appear few hundred meters on the projected map.

And the differences between the data stored and the projected map when using lat/long.

Thanks!

EDIT

This may be more specific to China and the infamous offset issue.

Looking at the following coordinates: 31.230548,121.470965 for the Shanghai Art Museum on Google Maps and ditu.

Having entered the same set of coordinate in OSM, it gives me the Shanghai Art Museum is about 400M away in the NW direction.

I don't understand why a physical point in space is different on the projected maps? Is this specific to China?