hYm3nSl4yru can defo push through a choke if the enemy demo fully unloads for no reason
Yes, but the word "advantage" is either used in its normal, dictionary definition (such as describing the advantageous position you have when the enemy is out of ammo), or in a special TF2 definition - what I take this survey to be asking about.
When someone says "we have advantage" or "it is advantage," in the TF2-specific sense, it almost always means that you have more Uber charged than the enemy medic does, and it is enough that you can actually play around it in the current position.