The speaker is saying this in what I would take as a form of astonishment at how fast the students moved the wooden logs out of the warehouse.
In the sentence is a noun, 意外, meaning "unexpectedly" or "surprising", and an adjective 早かった "was fast". And a sentence ending particle. Lastly, the unsaid subject is the activity of moving the logs.
I'm unsure of what the と particle is doing here though. This isn't a conditional and I know that と is used for quoting things. I also know that those things don't necessarily have to be said either. They can be thoughts, sounds made by actions or the manner in which something is done. Would this be a case in which the と particle is "encapsulating" the manner in which something was done? If so, what purpose is と serving? It seems to be used in an adverbial sense. I don't believe this to be と's "and" or "with" usage for keeping a reciprocal relationship with the subject either.