How did this happen?

I was playing a player who was wall knight, on round 3 they played a cosmic flower and then played 2 photosynthesizers on top of it. How did they do that when photosynthesizer costs 1 sun? They hadn't played any other plants or environments before that, I'm not sure if they played any tricks though (sometimes I don't always see the animations for my tricks that I play, so maybe something like that happened, or I just missed it) but what trick would give them 2 photosynthesizers to play for free? Either that or a cosmic flower that costs less to play?

edit: it's possible they played a plant in round 1 or two, I played a firework zombie in round 3, so if there was a plant there, I destroyed it before they played the cosmic flower, which means it was likely a plant with 1 health, or I used one of electric boogaloo's tricks on it and/or then destroyed it with the fireworks zombie.