I've been a web developer for decades. What you are describing matches nothing I've ever heard of on any browser or platform. This indeed was an html page that redirected to a pdf after clicking a link. Nothing about this should trip up any modern (or ancient) web browser. Absolute basic functionality.
Why would I be lying about this?
You tell me why you keep insisting a normal web page is like greek to your phone. Or why you were required to login to google services -- something neither the webpage does, nor any OS-oriented handling of any actually-unknown file type I have ever seen on android (ps HTML is not a bizarre unknown content type). What you described (in two distinctly different and random ways) sure isn't anything I'd ever be able to explain.