Even if they can handwave it away as not technically being a direct contradiction, it still doesn't jive with the intent and tonal presentation of what is said in ESB.

Obi-wan's choice of wording implies that Yoda instructed him one on one, the same way that Luke is taught. ESB also shows Yoda being a hermit, who meditates and lives peacefully away from civilization. The prequels show him as essentially a public school teacher for young children, living in the big city. It's a jarring inconsistency, and it just doesn't feel right.