Connection between the two- that is the question. Ultimately the throttle plate in the carburetor controls the engine speed. And they do sometimes come loose on these. You can inspect it easily by removing the upper shroud and the elbow that is held to the end of the carb. The governor assembly inside the engine is what controls the linkage to the throttle shaft. So if all else looks good, that should be your answer. Too much oil (your sump is about a quart and a half) can be a bad thing and cause lube issue. Though it very well could have been the luck of the draw. Another note is do you know that it was overfilled or could what you saw was fuel had also entered the sump and raised the level?

Focus on what Tom states about the possible throttle plate issue.
Failure to address that concern can lead to serious engine damage or total destruction. Click link below for a case in point.

Here is a link that might be useful: throttle plate came loose

I'd also check the carburetor/governor linkage.
Sounds like it might be binding.

Thank you each for your posts. I am in the process of checking the issues you mentioned one at a time.