Even if you would like to use the pregenerated bitstream, you need to follow all the steps in the example. This means that you have to run SoC Builder with the Build Model option first.
After clicking the 'Build' button in SoC Builder (step 6), your SoC project folder will be populated to look like this:
(Notice the socsysinfo.mat file. This is the "project information file" mentioned in your error message. If your project folder does not contain this file, SoC Builder will not recognize this folder als SoC project folder.)
The idea now is that during step 6, you can abort the synthesis process running in the external shell, and instead copy the pregenerated bitstream into the project folder above and load it onto the hardware using the 'Load and Run' button in the last window of the SoC Builder.
Now that you have run the SoC Builder once with the 'Build Model' option, you should be able to use the SoC Builder in the future with 'Load existing binaries' and the existing project folder. The SoC Builder will then jump directly to the 'Connect Hardware' window.