Of course going from a state of no-speaking to speaking would improve your ability to speak. This is because when you get to that stage, there’s often two ways you correct yourself:

1) you have so much input already that you can hear when what you’re saying is wrong, so you gradually adjust more and more for the future 2) a native speaker will correct you, so you adjust for the future

You seem to have most likely relied on the former. Studying accent and shadowing would have diminished the amount of times that you made mistakes during that time.

So your error reduction was actually both — getting input, and starting to output, and gradually making less mistakes.