This was a short story I read. The Earth people were impressed by the alien’s technology, but it turned out that the alien was only a child and had no way to communicate anything of importance about his home planet, nor could he get home.
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1Can you remember roughly when you would have read this? If so you can edit that and anything else you can remember into your post. – TheLethalCarrot Feb 18 '20 at 12:46
The old Theodore Sturgeon story Mewhu's Jet has this plot.
It ends
"Much good will it do us - and him, poor kid. With a kid's faith in any intelligent adult, he's probably been sure we'd get him home somehow. Well, we haven't got what it takes, and won't have for a long, long time. We don't even know enough to start duplicating that jet of his - and that was just a little kid's toy on his world."