You're reading that in to his comments. He's just said that they'd both be out for a long time. Doubt they'll be out for the same amount of time, but we'll have to wait and see.
From BBC:
On those "injuries", Brighton manager Roberto de Zerbi confirmed that winger Solly March and forward Danny Welbeck will be out long-term:
"Unfortunately, it’s a very tough injury [for March]. We lose him for a long period and Welbeck the same