Did you know this? Harry Potter related!?

Okay, so All the Weasley's (there are 9 of them), Harry, Hermione, Tonks, and Sirius were all sitting at a table. (That's 13.) Sirius was the first to get up. Sybyl Trelwany- "When thirteen dine, the first to rise is the first to die." Do you think JK Rowling did this on purpose?