I reached out to Matlab directly and after some troubleshooting we found the source of the problem: when following the offline install instructions to download the Support Software Downloader for the online machine operating system, it was downloading the corresponding third party installer package, i.e. the Windows UHD install package rather than the Linux.
The solution was for me to use an online Linux machine (used a VM on my Windows computer) to download the Software Support Downloader and therefore download the Linux UHD package.