Most of Reddit knows about voat - there were multiple frontpage posts about it. So, if voat was open, the migration (however short it may have lasted) would have probably been much more visible. There was also a very popular thread about alternatives, as well as an entire subreddit for it (/r/redditalternatives) - Redditors really had no need to google it. So I don't think search trends are a very accurate estimate of how many would have left in the right circumstances.
Yes. We had one reddit influx a while ago was due to a mention of "hubski" without a link in a top comment on a top askhubski post. The influx was remarkably smaller than any others that we have had, even though the visibility of the post and comment was higher than most (if not all) of the links we have had on reddit. However, traffic we got from google searches for hubski was insane whereas when people link, the user comes directly from reddit and the number of people who show up is so much higher. Redditors really had no need to google it.