Pretty much agree with what has been said. Also remember that the Salamanders have the hardest initiation of the astartes. Though in our point of view we could look at this number and say they could have still been able to restart a legion, the other part is the fact that the Salamanders probably wouldn't have gone on a recruiting spree due to their ideology and doctrine.*shrugs*
I'm only suggesting a way in which it can make sense. Plus there are only so many ways they can say things. At the end of the day, it is surprising (from the 30k pov) that the three loyallist legions survived to the 40k timeline. They theoretically shouldn't have survived; i'd have considered (in horus's position) to annihilate Medusa, Nocturne and Deliverance rendering them permanently disabled.
The 'fatal' part likely refers to the 14000 replacement astartes being completely untempered and battle experienced, compared to having 250 year old combat vets.
I do see your speculation, however its also important to note that new fluff has been implored to make things more plausible for the 40k world. Now we can see how possible it is for the Salamanders to make successor chapters.