The ability of emmersed plants to absorb ammonia from the water is really great because they have constant supply of CO2 from the air in big amounts, so the water quality in that vase may have been fine actually, but in a vase....come on...unless it's a big vase..
Although I've got small tanks myself, if I had a way I'd ban the sales of anything less than 20-30G
As for beginner's safe fish, I am afraid there're none. They'll all suffer their share of beginner's mistakes, the question is which one will survive. I guess some fish are just not as sensitive so certain levels of toxins compared to other's or luck comes into play.
And keeping fish that grow too big for the size of the tank and taking no notice is not even animal cruelty, but just being pure stupid and ignorant. There's no excuse to be honest.
But we humans have sick twisted minds to the point that even keeping birds in cages has become like a pure normal thing no one takes any notice of at all. If one has to be honest, birds are supposed to fly, don't they?
Sorry, I think I feel better after letting it out of my chest