Surprisingly means in a way that was not expected. The result is not what anybody would have guessed.
It works before an adjective, giving surprisingly good, surprisingly cheap, surprisingly few, and there it means more than you would think. It also opens a sentence, with a comma, to flag the whole statement as unexpected. The negative is a favourite of British writing, since not surprisingly means exactly what you would expect, and it is used to make a point look obvious after the fact.
1adverbsurprisinglyIn a way that causes surprise.
“The room was surprisingly warm.”
From surprising + -ly.
Etymology from Wiktionary, CC BY-SA