i think the pick up Card is just a Monster Card of the deck, that could be any Monster Card in the deck and it changes every time you choose you Opponent. I duelled against the same Player (friend list) 2 oder 3 times and he had the same deck every time but the pick up Card was another every time.
It’s the first monster card that is on the top left spot in the deck editor. It’s purpose is to give you a hint on what deck your opponent is playing so you can counter pick a deck to beat it.
Pick up card is the card that is most useful in the deck. Like my deck is made for Blue Eyes White Dragon, like I have pretty much every card able in some way that would boost up my Blue Eyes.