Left-handed people have to write from right to left instead of left to right. But right-handed people write from left to right. So since he was left handed, he tried to write like a right-handed person but he ends up writing backwards.
If you would slice the bread right in the middle in half. You now made a reflection. The triangle is naturally reflected by the 0 in the x-axis. The snowflake is naturally a reflection.
Since he is naturally left handed, he can sort of write backwards naturally. The backwards way of right is left so us left handed could write better than right handed people backwards.