When I download this website, I can see that HTTrack is creating folders with
the images. So technically the images files are downloaded. Perhaps you can
inspect your downloaded folder structure too. For example there should be
subfolders labelled for example "boards" and "cabinets".

However, the website is done with PHP and in my downloaded copy the files end
on .php file suffix. This results in my case that .php files are obviously not
interpreted and the browser shows the ".php source code" instead of the
expected website.

A renaming of .php to .html works and then the webpage is displayed. However,
that works only when you drag and drop each single .php-to-.html renamed file
into the browser.
As when I start with index.html, contained references are referencing out
again to .php.

In order to make that perhaps working more nicely, all .php file contents
likely need to be searched-replaced .php to .html also in each single file.