I am in total agreement with that. Actually, their technology would seem more like straight-up unadulterated magic rather than scence fiction. I can just imagine if someone from 900AD (let alone 300 BC) materialized in New York, or Dubai, or Tokyo! He couldn’t even begin to describe what he saw ....reminds me of the part of Ezekiel of the spinning wheel. Hmmmm
I agree with that. As you stated in your example, imagine someone from the year 900AD arriving suddenly in the present day. Even the simplest things (that we take for granted) would be utterly confounding and totally mind-boggling to them.
I think such a person would overwhelmed to the point of terror at the (seemingly) magical quality of everything in our world.
Now, take any garden variety human from the 21st century and propel them forward in time to the 31st century, and you'd likely get the same reaction. Technology of that time will be so advanced beyond what we know today, that we wouldn't even have a context in which to understand the most ordinary things. Just like someone from our distant past would experience in our world.
I believe it's very shortsighted of people nowadays to believe that faster-than-light travel is impossible, or that in all the vast universe, we're the only intelligent species with advanced technology. Logic and reason compel me to take the position that the universe is teeming with intelligent life, and that many civilizations exist that possess technologies far in advance of our own.