Turnips that have just matured do taste a bit like potatoes.
But older turnips that were left in the ground longer or those turnips that have set out longer after they matured taste a bit more bitter and will sometime smell sweet when cooked.
The turnips may also have an earthy taste to them depending on how old they are.
But every time I've grown and picked my turnips they tasted similar to potatoes.
I like to sometimes cut up turnips and make turnip french fries which taste pretty good as well.
Although raw or steamed or just cooked turnips are better for you than fried turnips.