"Subsidy" carries a connotation of purposeful action to help something. Subsidizing a bad thing is worse than merely allowing it to happen or looking the other way. It seems like you want to re-label things in "B" by the label for "A" to make it sound worse.
Purpouseful action implies awareness and intention.
Externality implies not yet recognized.
Having 2 words for similar concepts does not mean they are different concepts. "heavy" and "massive" are two different words but they convey essentially the same thing.
I would agree that unrecognized externalities are not subsidies, say CO2 pollution before it was recognized, but then again since they were literally not recognized as externalities (yet).
But the very moment CO2 pollution is recognized, the previously unrecognized externality is to be instantly viewed as a subsidy.
History repeats itself, the first time as a tragedy, from then on as a farce.
There are direct and indirect subsidies. Indirect subsidies include externalities: external costs paid by everyone else (that the government should be incentivizing reductions in by requiring the folks causing them to pay)
Semantic digressions aside, they're earning while everyone else pays costs resultant from their operations (and from our apparent inability to allocate with e.g. long term security, health, and prosperity as primary objectives for the public sphere)