The tweet is wrong. I think its safe to assume the author means 'open' for ope as well - another typo.
He said the 8th, she wrote the 18th and both are clearly incorrect. As she goes on to say in her next tweet, Reeva's birthday is the 19th.
Perhaps the person who heard the 8th was wrong. Both are wrong, but it seems 18th isn't as far off as the 8th. Someone heard wrong, but who?