Not a Deckbuilding Game

[Albie There]

How is this a deckbuilder game?

You don't unlock new cards, the cards each character have are "hard coded" to them, when you start a new game you start basically from zero, you are not collecting cards, only during a run. So there is really no progression that makes the game easier each time.

You just have to get lucky with the RNG to win a run so basically it's seed spamming until you get good cards.

[Buntkreuz]

A deckbuilder is simply a mechanic that means that you grow your deck of cards with new cards while playing.
Thats it.
Nothing of what you mentioned is part of a deckbuilder.