I definitely used 7zip to unzip the file, and placed it in the platform-tools folder. When I had it unzipped directly into the folder, it placed it in its own folder titled the same as the file (frida-server-16.1.3-android-x86). When I had it like that, it would give me the 'is a directory' response when I would do the very last step as such:
/data/local/tmp/frida-server-16.0.2-android-x86
I then tried unzipping the folder and placing the file directly into the 'platform-files' folder. This time, it gave me the same 'is a directory' response when I did the step right before:
chmod +x /data/local/tmp/frida-server-16.1.3-android-x86
So unfortunately I'm not sure where I'm going wrong. Every step up until that point worked exactly as the guide.