I think that's the expected behaviour, as antimatter is not a status, but a change in stats. The card says that it will deal one extra damage per 5 quanta. In this case they are dealing 14 - 5 and 14 + 5. That is, the base damage plus a bonus of 14.
Incidentally, this effect can be a fun way to bypass shields, though this is much more useful with a dune scorpion with -1 attack than it is with a fahrenheit.
This is pretty awesome. I wonder if it is another part of the reason behind 75 quanta cap :p.