Lol, I don't know why he said that but the Edonia sections takes place months before the outbreaks in China, and there is no outbreak in Tall Oaks yet so Leon doesn't even know Helena exists. I thought we already discussed that the Edonia section took place six months prior to the outbreaks in China in this thread, I could be wrong.
Well you can see if you look closely at Pier's mobile in the bar scene in Chris' demo that all his comrades deceased on 24. Dec. 2012 and in the beginning it is shown that this scene is happening in June the 29th 2013.
So apparently there is a timegap.