There's no information about that, so presumably given the slant of the article it was an innocuous invitation.
I have tried to find any other references but haven't.
It is not unusual for members of parliament to be invited to other countries, so information needed would include:
- who specifically invited AfD
- was this invite open to other parliamentarians
- what was the nature of their 'invite'
- was this part of a broader diplomatic program (such as China's invites to EU representatives and diplomats to tour Xinjiang)
China would deal with AfD just like they deal with left, right, far right and theocratic governments and absolute monarchies all over the world.