Answer: Yes they are different plants, but it gets confusing very quickly. Brassica includes a wide group of plants -- take a look at this list, for example.
Interestingly, the cole crops are interfertile which means they can cross -- whether your seedlings are the result of that or the reversion of the hybrid parent, I am not certain. It might also be that you are looking at a wild mustard plant or a cross of that.
But, your broccoli-raab is a distinct plant.
Rape is yet another plant, Brassica napus.
And broccolini is apparently the result of a cross between broccoli and a Chinese kale.
You may find the following discussion about broccoli (and its parenthetical mention of raab) interesting. You may need to cut and paste the complete url into your browser to make it work correctly.
In any case, your plant should be edible so you could experiment and see how it cooks up. I hope this helps!
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