There is an intended agent experiencing surprise, and we might under some circumstances agree that we know who the agent is (just as we expect that "the experiment was conducted" by the author as researcher).
But, technically, the agent is obscured and not written, so we can't be completely certain about the writer's intent. Maybe Rosalind Franklin conducted the experiment: we are only led to infer that the author was responsible.
Personally, I generally understand "Surprisingly," to mean "An attentive reader should now be surprised that...".
There's an expectation of general surprise relative to an earlier claim in the text; the writer assumes the reader will be surprised (whether or not the writer was truthfully surprised). I find myself annoyed by this style, whenever I am unsurprised.