When a HTTP client wants a resource, it issues a GET request. If it after retrieving the response saves it to disk or just keeps it in memory while it is viewed in the browser is irrelevant. That is not a concern that the HTTP protocol is designed to deal with.
So saving a page for offline viewing shouldn't be easily distinguishable from just visiting it. The browser might fetch some of the resources again if they are not cached localy, but that would look no different to the server than if you had just reloaded the page.
That said, it might be possible to detect a "download" by doing some carefull traffic analysis, looking at timing or whatever. But that would require quite some work and would be highly dependent on what browser you are using, and I find it hard to believe anyone would ever think it was worth the effort.
So no, I wouldn't worry about the owner of the page knowing that I specifically downloaded it as opposed to just viewed it.