That's why I called it the simplest explanation. You have 12 populations of bacteria. One of them, after quite some time, suddenly displays a new ability that the others do not. One explanation: they acquired that ability. Another explanation: they always had that ability. The former explains the observation with a single factor. The latter, though, requires you to not only explain why the latent ability suddenly got expressed in that one population, but why, under identical conditions, it didn't get expressed in the other 11.
You might be right, of course. The proponents of the former explanation are busy looking for exactly how and when the new ability was acquired, as they should. If they find out, they will presumably be able to show that the whatever-it-is does not exist in the other populations. Meanwhile, proponents of the latter explanation should be expected to look for where that ability was located before.
Since that has never, ever happened before, don't you think it just a wee bit optimistic to think that this will be the very first time?