Thank you for your question and for including such a clear example.
You're quite right that the caret sign indicates a key-press on a calculator.
Now, there is a section (113.d) in the Nemeth Code that gives rules for transcribing a keystroke indicated in print by a sort of key/button shape with material inside it. However, in this case, print is not using any shape to indicate a key-press. So, I would follow print and present these representations without "keystroke" indicators.
For the caret, I suggest you do not braille it in a superscript position. Rather, its meaning will best be presented by keeping it on the baseline, as in the attached .BRF.
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