Today, a person said that he was from China Mobile and wanted to give me free data. He sent me a verification code and asked me to tell him that I later realized that it might be a scam?

The questioner did the right thing. Since you didn’t tell the other party the verification code, of course everything will be fine.

Giving free traffic is indeed a thing. Generally, your own customer service (each mobile user has his own customer service) communicates with you. If you ask for a verification code at this time, you can still give it. But they were all communicated over the phone before. My customer service added 10G of national traffic every month for half a year.