"...was conducted" suggests no information about the conductor. It could be the author, and in the specific context of an academic paper it implies the author, but it could just as well be anyone else on Earth especially outside of this context.
"Surprisingly" (or "the results were a surprise," etc.), on the other hand, doesn't leave anything to the imagination. I can't think of a way this word could potentially mean that another party but the author was surprised.
Passive voice could hide the party responsible for surprising someone (active "Alice surprised Bob" becomes passive "Bob was surprised"), but in the original scenario, the party causing the surprise (the subject, which could be hidden by passive voice), is the experiment. The surprised party is the direct object, not the subject... passive voice is not a term to describe hiding the direct object; that's transitive versus intransitive.