They probably were aware of both technologies.
However, these technologies are unproven. So they had to assume we would try to solve the problem with known solutions while still spending on R&D for future, better solutions.
Thus, they stated they weren't sure if they could eliminate farting cows and airplanes fast enough. Right now, it's not technically feasible.
There is a lot of research that must be done before we can figure out if the seaweed is a viable solution to cow methane. Among other things, we have to figure out if we can grow enough of it and if it changes the beef and milk in any way.
And like I said, we need a breakthrough in battery technology before we can build large electric planes. It's a power versus weight problem. Today's lithium ion batteries are very heavy.
The one thing they did get technically wrong in the FAQ is that the problem with the cows is belching and not farting. But "farting" makes for better humor.