I've seen this rumor online a few times now, such as:
Can Vietnamese people break apples in half? (1,247 views)
Yes. Source: half Vietnamese.
The claim also seems to be on Reddit (here; here; here) [I can't access Reddit from China right now: VPN is not working]. For this rumor, there's something special about Vietnamese people in particular; it's more than just "some people can do it, and some people are Vietnamese".
Question: Is it common for Vietnamese people to be able to split apples in half with their bare hands?