The answer is correct, although it’s a pity that the error is there.
If you use the One-Click installer https://anirudhsanjeev.org/projects/oneclick/ with the download link at www.ads-software.com, then it automatically puts in the wplistcal subfolder. I guess that’s because the zip file is a zipped folder rather than a zipped file collection.
Either the files should be zipped without the folder, or the plugin code should assume there is a containing wplistcal folder.
