Then you haven't been to China. It's a shorthand gesture there. The character for ten is 十 so I'm not sure if the gesture informed the character or the other way around. What is noteworthy is just that both cultures ended up with a cross to denote ten.
I'll admit, I thought "I'm sure I'd have heard that before if it was true", but it appears to be the case! It's apparently based on a gesture Leonard Nimoy saw during a blessing as a boy.
I guess it's like the ICXC hand shape that vicars and priests use in Christianity.
These religious leaders and their hand gestures...