Although the documentation suggests that digitalWrite() needs to take the values LOW or HIGH (0 or 1) as arguments, in fact any non-zero value will do for HIGH. I haven't looked at the source code for this function, but it will be faster to implement
"if value isn't zero then make the pin high, else make it low"
rather than
"If value is one, make the pin high, if it's zero, make it low, otherwise what should I do??"