Great. Example of callstack: when you type a URL in your browser, it tries to generate a website request. This request is inspected by scanning engine (e.g. Avast), then it may be examined by Firewall, when this connection is allowed, then it may be inspected by other component(s) and when it reaches the lowest device (your physical network card), then this request is leaving your computer.
Web browser -> Avast Scan -> Firewall -> ... -> network card
when the website request processing fails in Firewall component, you'll see all previous layers (in callstack). That's why you see Avast in callstack, although this request has been already forwarded to next layer. It's good to see callstacks, because you know which layers inspected (and possibly modified) these requests.