Is this considered cheating?

This happened like years ago, but I am petty and I need to know if this is cheating. So one time, I was playing uno with my brother, mom, and the neighbors daughter, who we’ll call Lucy. So we were playing with this house rule where if you call uno on someone and they have more than one card, then you have to draw a card, so anyways, my brothers, mom, and I were all playing holding our cards in our friend, while Lucy had her cards sorted in piles by color and these piles were BEHIND her back, and out of my view, I also happened to go after her. I thought it was weird that she wasn’t holding her cards but I was like whatever, maybe she just has a lot of cards. There was this point in the game where the thing was a certain color (we’ll say blue) and Lucy only had 2 blue cards left, so she grabbed her blue cards and played one, I had lost track of how many cards she had and all I saw was her holding one card and not saying Uno, so I shouted out “Uno!” and Lucy look confused and she was like “I have more than one card” I pointed at the card in her hand and said “You only have one, and you forgot to say Uno!” So she leaned to the side, revealing the massive pile of cards behind her (she had like 20) and then told me that I had to draw, so we started arguing, me saying she can‘t keep her cards behind her, and Lucy saying that it was fine and I had to draw, now Lucy is a couple years younger than me, so my mom said “Just draw the card [my name]” so I silently drew the card. I am still upset about this and need to know, is keeping your cards behind you cheating?