"Indian Summer" fills the air with good vibes instead of lyrics. This is another track where the vocals are distorted and the pitch is raised; currently a very popular trend in the EDM scene. Producers utilizing this editing style have seen fans flock to the new sounds. It’s quite similar to Bearson’s phenomenal track "Pink Medicine" or something Jai Wolf’s label mate, ODESZA, would put out.
Generally, the music accompanying the unrecognizable vocal sounds also keeps the mood light with a feeling of hope, optimism, and a luring sense of adventure. Personally, I think these types of tracks are making an impact due to their open storyline. The music definitely takes you somewhere, but it's up to your imagination to figure out where.
I'm sure there's a whole science behind why the raised pitch and distorted voices are attracting listeners, but for now, I'm good with just knowing these tunes exist.