First, according to the conservative Frankfurt newpaper FAZ, it was only one terminal that got evacuated, not the whole airport (the terminal used by LH for their domestic and inner Schengen flights, therefore no passport check after the security check).
One person pushed through the security check before it was completed. There is no bomb threat.
According to the article the evacuation was going on peacefully, no panic.
As it is standard practice, the whole area is now considered to be contaminated and has to be searched, and every person in it has to undergo a full security check again.. Therefore everybody had to leave the sterile area and go back into the public area.
Things like this happen several times a week across Europe, mostly it is late passengers, who want to catch a flight. The person will certainly be caught, arrested and fined, even if they did not carry anthing dangerous on them. If they had anything like a weapon on them, they will go to jail.
Our Royal Green Jacket and the Daily Wail are sensationalising again.