Best practices for uploading a bought or free track
Downloading a track (or purchasing it) does not transfer the right to you to upload or make it publicly available on SoundCloud. You'll still need permission from the copyright owner(s) if you want to make their music available on your profile, even if the copyright owner has made it available for free elsewhere.
How about checking if this creator has an official SoundCloud account? If the track is already published there, you can repost it to your own profile or add it to your Library.