The gene that was added is translated into a protein that floats around the cell doing the RNA demethylation. The plants already have other genes that produce proteins that did that, but adding another one has an effect.
I'm surprised the plant lives at all in that state... One would imagine RNA methylation is used for all kinds of logic and mechanisms in plant cells, so arbitrarily removing them all would break stuff.
It would be like a programmer saying "let's just comment out every line of code starting with "if" in the windows source code, and then see if it boots faster!
Edit: correction - thanks Scaevolus, my mistake.