Points and Coordinates

Someone sent me the extract below to criticise:

Points? x, x+i could at most be coordinates of points instead, is it not? A point in the Cartesian plane would have two coordinates: one to tell us until where we walk in the horizontal direction and another to tell us until where we walk in the vertical direction to reach the point. 

i should be regarded as a reserved letter, since, with it, we denote imaginary, the square root of minus one. In this case, we only use it if we really mean that. They couldn't have meant imaginary there because they are talking about two generic points instead.

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