I also downloaded your file and when i unzippped it by using Winrar i just get the data folder and the readme file.
But there is different methods to unzip a file. If i just click the zipped file it opens up in a new window and from that i unzip. This method will only give me the Data folder. But this is the most standard method to use and this is also the way many modders use.
But if i right click the zip file and choose from the dropdown meny to unzip the file to Keldunks_RFB1.52_tweaks it will create the folder where the data will go
Many people dont know about this method