The quote is saying that transmission line capacity is higher when it's windy and lower when it is windless (due to less cooling).

If you assume that EV charging is the marginal load which would put you over the windless capacity, but not the windy capacity, then in order to prevent overload you'd need to prevent EV charging when there is no wind and therefore the transmission capacity is lower.

Taking a step back it's a general problem with this type of optimization, what to do when the system has become accustomed to, and is designed for, capacity which isn't available. How do you get people to use less power in order to avoid a blackout?