Pretty sure that's just a derivation from everyday handwriting. The i-dots and t-crosses are two typical elements that can't be written without lifting the pen,

Pretty sure that's just a derivation from everyday handwriting. The i-dots and t-crosses are two typical elements that can't be written without lifting the pen, so it's quite a frequent thing to put pen to paper, write out a word that includes i and t but leave them unfinished so you can continue the rest of the letters in one fluid motion, then go back and finish them off by dotting and crossing them. Hence dotting is and crossing ts is going back to do final touches that you've neglected or may have missed while working quickly or casually.