His methode is unsuited, because he need two separate and also timely separated reads to identify the key: First he must put the columns low to read the row code, then he must determine from which column it came. What, when due to bouncing he finds a different column or even all columns to be the source of his row code??

Also, when he touches occasionally two keys in combination with bouncing, then he can detect neither the first nor the second, but a third, phantom like, which sits at the corner point of square, formed by the two keys!

He cannot handle at all when two or more keys are occasionally pressed. The other methode with only one column set low at a time can. Also, how simple the debouncing by the help of vertical counters is with the latter methode, and the handling of wanted and unwanted multi key pressings...

Kai