Greetings KR welcome to the Forum.
I don't know what that guy's talking about !
Sure you can Caulk the Glass.
You said that the water was running down the door, and into/thru the Threshold ?
If that's the case too, they make a strip of shaped Aluminum that you put at the bottom of the Door outside, and it sheds the water away from the Threshold.
If you've never seen one, think of a Metal Cover over a outside Door, but in miniature and it goes across the width of the door. They come in different depths, and you choose one that will drop the water sufficiently away from the door, to keep it from entering the house.
Have a good Day !
S.W.