USA to Shenzhen to Hong Kong?

Hi,

I'm a US citizen planning to fly from the USA to Shenzhen -- and then take a train to Hong Kong after a day.

Do I qualify for the 144-hour policy if my onward ticket to a third region is for a train, rather than a flight? I'm pretty sure that is what this article says, but I just want to confirm.

Thank you very much for your help.