Not really. E sharp is the “F” note on the piano, but in a musical composition the key signature can indeed contain an E ‘sharp’ (which will be played as F). Probably Blue Knight was singing a song in which the key contained an E sharp and that’s why he (I presume it’s he!) termed it 'E sharp. Likewise, an F can indeed be ‘flatted’ in the key signature (and would be played as E natural.
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