Conversion table stuff being wrong is common. As has been brought up before, the US does not us Imperial System and never has. The US uses the US System of Customary Units. Most are the same, but some are not. This is why Festool calling their US tools with inch labeling is Imperial is just so silly. They are for the US, but not Customary? Just shows the sorts of confusion that happens.
Liquid stuff is bad because so many don't know the Customary units, teaspoons/tablespsoons/pints/quarts/etc. Older folks know how to go between them, but as you go younger, no one knows. Add to that the US half converted to metric when it comes to volumes, you never know what you are going to deal with. If something says 2 tablespoons, and you have a tablespoon, no problem. But if you only have a teaspoon, no idea how many go into tablespoon, or if that even works. I'd love to have all metric measurement stuff for cooking, but you can't find them, some are dual labeled, but you can be pretty sure one of those labels are wrong.
Then there are tons. It shouldn't be hard, but in the end, the whole world needs to retire all versions of "ton", as it takes so much work to hope you are all talking the same thing.
Not sure how much it impacts text books, most text books are metric only here. Unless it's a long running text, anything in a technical field is all metric, sometime half and half. Some will have some examples in customary units, often just to show why customary units are not used.