Why not? Fat-finger a number, then remove the number.

Here's the actual source of the story from the above screenshot:

https://apnews.com/article/fact-checking-537000968712

“While the ‘No’ vote was entered correctly at 11:19ET, the ‘Yes’ vote that appeared for 2 minutes on CNN was actually the ‘total’ vote of the combined ballots for Yes/No/ Santa Clara,” Farbman said in an email. “This error was entered at 11:19pm ET and corrected 2 minutes later at 11:21pm ET when we deleted the “total vote” in for ‘Yes’ and entered the correct ‘Yes’ vote.”

So yeah, it appears that the numbers were overinflated accidentally, and the drop in the numbers was the correction. Should have been x for no, and y for yes, but for two minutes, they accidentally showed x+y for yes, instead of just y.