This is true. My phone connected to 4g when I turned it on but then upon my first search using google now it disconnected and then reconnected to an H+ network and completed the search. It was pretty cool how they made a completely separate network for it.

With the caveat that in some countries the way data roaming works is all the data is routed back to your home before actually being routed to its destination - for example, if I visit Canada with a US T-Mobile SIM, all my traffic first has to travel to the US, even if I'm pinging a Canadian server.

If you end up with this sort of data configuration in China, you'll be having a bad time using it for anything performance-sensitive. Good enough for email though, I bet.