I thought lemonade was something different over there. And wikipedia agrees.

In the U.S. and Canada lemonade refers to a mixture of lemon juice, sugar, and uncarbonated water.
Whereas over here lemonade is:

Likewise, in the UK, Australia, and New Zealand the term mainly refers to a colourless, carbonated, sweet soft drink containing either natural or artificial lemon flavor, such as Schweppes Lemonade.
So ours is fizzy, yours is (apparently) not. Soco and a non-fizzy mixer would taste disgusting.