DNA alone is not plant or animal. It's effectively saying 1s and 0s can be vegan (or not). Pretty silly.
There's a strong parallel here how pro-life activists view the use of human stem cells.
And the pro-life activists certainly have a similar argument. They're also welcome to holding it, as long as they don't impose it on others.
But as long as they themselves just stay away from stem-cells derived products, then it's their own personal choice. I also have no problems with, for example, Jehovah Witnesses that refuse blood-derived products.
If they have an ethics code, they are welcome to follow it, as long as they don't try to impose it on others.
In this particular case, accommodating even a maximalistic vegan position was not a big deal (just use hemoglobin from plants), so why not do it?