Not necessarily. Speach and language develops at different rates in kids and I can totally see a moderately advanced two year old using a complete simple sentence.
Most 2 year olds can combine 2-3 words at max. They have no idea of the concept of other planets, possibility of leaving our own planet etc as the OP implies. If you have an article or a paper happy to be proven wrong... but all internet searches so far point me to not believe you.