Re: Rigged or bugged arena game

No, it is not rigged nor bugged. 

To unlock Aqua Vine, you will need 250 seeds.

From your second image, it shows you have reached 173 crowns so far and have earned the rewards of 20+40+50+60 seeds, this totals to 170 seeds so you are 80 seeds short.

You will need to carry on playing to reach the next Aqua Vine seeds reward at 500 crowns (for some reason, the amount of reward of seed is not state, but from past experiences, it is 80 seeds) to get more seeds so your total becomes 250 to enable you to unlock the Arena new plant.

TLDR.  You need to reach 500 crown points to unlock the new plant

EDIT:  I have just noticed your third image showing 0 seeds. 

Question do you play your game on another device? 

I ask because on update 11.3.1, there is no Aqua Vine in the Almanac so the seeds reward jumps to the first plant which is Peashooter. 

If you only receive Peashooter seeds, this means you have been playing with an outdated PVZ2. (11.3.1)