GPT-3 handles idioms just fine. Here I tested it on "I fell for her." https://files.catbox.moe/lp6oyg.jpeg
"Poverty of the stimulus"
How does it do with "I fell for it?"
So I would say that, while you may have never heard it used that way, it certainly has that meaning in practice to many people. Don't judge the robot so harshly.
[1]: https://dict.leo.org/pages/addinfo/addInfo.php?aiid=En842ho0...
[2]: https://dict.leo.org/pages/addinfo/addInfo.php?aiid=EKHR2Car...
[3]: https://dictionary.cambridge.org/dictionary/english/fall-for...
[4]: https://dictionary.cambridge.org/dictionary/english/fall-for...