The “fake meat” they are referring to is lab grown from the living cells of animals not vegetable amalgamations made to imitate meat.
Depending on an individual’s reasons for following a vegan or vegetarian diet, lab-grown meat may very well be okay.
If their reasons are nutrition based, sure, they should avoid lab-grown meat.
If their reasons are based in the ethics of raising animals for slaughter, factory farming, or the carbon footprint and/or food and water waste involved in raising an entire animal just for parts of it to be food, then lab-grown meat might be fine in their mind.