No, your friend's play was not legal. Turn Aside counters spells that target permanents, but a creature spell is still a spell and not a permanent yet.
A spell is (generally) a card on the stack. It remains there until it has resolved or been countered.
112.1. A spell is a card on the stack. [..]
A permanent is a card or token on the battlefield.
110.1. A permanent is a card or token on the battlefield. A permanent remains on the battlefield indefinitely. A card or token becomes a permanent as it enters the battlefield and it stops being a permanent as it’s moved to another zone by an effect or rule.
A spell is never a permanent, and a permanent is never a spell.
Essence Scatter targets spells, never permanents. Since Turn Aside can only target spells that target certain permanents, it can't target Essence Scatter and your friend's play was illegal.