"Logain? That must be the false Dragon. It was the first time Rand had heard a name put to the man. Lan sounded almost as if he knew him."

(EotW, Ch.14 p199)

"Sleepily he (Rand) wondered if Lan really did know the false Dragon."

(EotW, Ch.14 p201)

This is almost too clear to be true, but let's assume that Rand is right about this: Lan has met Logain before.

Logain was born in Ghealdan in 972NE so the odds are that Lan did not meet him until after he became Moiraine's warder...a 7 year old boy from Ghealdan would not have been anywhere near any fighting during the Aiel War. Logain began channeling sometime around 993NE (in LoC ch.52 p934 Egwene states that he's held off the madness for 6 years)and it is not unlikely that Moiraine might have thought him a possible candidate out on her quest for the Dragon Reborn. Being who she is, she would have followed any report of a young male channeler- in 993 the Dragon Reborn would have been only 15, but he might have started channeling early...so, better not to take any chances. Once she meets him though, she quickly discovers that this one is too old to be the one she is looking for and leaves. An Aes Sedai's interest in him might have given Logain some interesting ideas though, ideas which eventually lead him to proclaiming himself. OR...knowing that the Black Ajah and other Darkfriends would be after her future charge, she might even have decided to...subtly prod him a little in that direction, set him up as a decoy. Wouldn't that be ironic if in fact a Blue Sister turned out to be the one who set Logain up as a false Dragon?