Not a silly question at all. Yes, autofocus is achieved with this combination because the lens doesn't communicate with the Canon parts. Canon sees only f5.6 and attempts to focus.

The results are not perfect but quite usable. I find the lens chatters before choosing a steady focus. This delay is a huge pain for an in-flight shot, but no big deal for a "sitting duck".

All that said, the in-flight shot of the Green Heron was a matter of luck. I doubt anyone could manually focus on that fast-moving target, or that any camera/lens combo could either. Look at the grasses either side (closer/farther) of the heron. How could an autofocus pick out what the photographer wanted? I expect the autofocus settled on a piece of grass that was conveniently the same distance away as the heron.