It's a guess, but my thinking is that previously most people who searched term hydroxychloroquine were mainly scientists and other people related to that not your general population. Suddenly covid happens and now large numbers of people learn about this new drug they never heard before, they are gonna search, and I presume this, most wildly different things like: "how does it work?" "does it cause some disease?" "insert something political here about hydroxychloroquine" "did aliens make hydroxychloroquine?" and many more things I lack imagination to come up with and that's only about hydroxychloroquine. I doubt 15% number is about single word cases, but more about combination of words and that seems reasonable. Inventing new words daily seems unlikely, chaining them on the other hand seems plausible.