For obvious reasons, when the price of bitcoin is going up, a lot of people are interested so they go to Google and search about it. So I think that's the logical explanation, imho.
But to say that investors will go to Google trends and make their decisions based on that is completely wrong. Maybe newbie investors will likely believe in this, but smart investors knows the game very well.
Well, this is just according to the majority of most searches using google but what about to those who surf anonymously? Although we can't deny the fact that Google is the most common search engines for people who do need to find a good result with just one press of that enter button.
Google searches may not be a good sign to rely on all of our hopes in the future since no one could ever tell what would be the future.