If I'm not wrong q2a blobs are cached, and yours not
If I open a question page (e.g. this one) from the question list (clicking on the link, here on q2a) the image the first time is downloaded from the server, the second time (same operation, go on the question list and click on the question link) is downloaded from the cache (do not do refresh of the question page or it will be always downloaded)
In your site I see it's always downloaded from server.
From a quick look the only difference in the response I can see is these "suspicious" header that your server sends back :
Cache-Control : private, no-cache, no-store, proxy-revalidate, no-transform
Pragma : no-cache