It is happening because it has more earning growth then gold and now every social, electronic and print media talking about it and more and more new people aware about bitcoin and want to enter in this market due to its huge growth.
That's right, Nowadays bitcoin is very important for people than gold, so it's natural that Google results show more people searching for bitcoin than gold, they knew the importance of bitcoin as an investment and a wealth, they also knew that the increase of bitcoin price is huge compared to the gold, that's why people are more interested in bitcoin.
Plus, what is now everywhere talk about it, people will know what it is, interested in the possibilities that it gives. Therefore, I am not surprised that people are interested in them.