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.
The old Theodore Sturgeon story Mewhu's Jet has this plot.
"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."