First, when the FBI said it wasn't a "naturally occurring strain" they probably meant that there was evidence that some sort of genetic manipulation had been done, indicating that it had, at some point, been in a laboratory. Whose, and where, is difficult to tell.
Second, there is a "natural" method of catching the disease if you happen to inhale the spores - this is "woolsorters' disease" and happens once in a very long time, say a decade or so. Twice in a week, and in the same location, is simply not believable as a coincidence. It is, of course, feasible that the patient could have sneezed the spores onto his keyboard, somewhat less feasible but still possible that his coworker could have picked it up that way as well. But the disease doesn't usually produce more spores inside the body, so it is more likely that they both picked it up from a common source.
It should be pointed out that we're not going to get an epidemic of anthrax out of this - the disease isn't particularly communicable in its pulmonary form. This is more like a poison...the problem is that the spores are durn near immortal and detoxification of an area they're released in is a very expensive process.
Smallpox is the other end of the spectrum - very communicable person-to-person, but not particularly communicable otherwise - the "infected blanket" stories that have been all over the 'net in the last week are pretty much just that, stories - one documented attempt was made to inflict the disease this way but it isn't too likely to have succeeded. Person-to-person, though, smallpox spreads like wildfire, and that could cause an epidemic, but won't poison an area as antrax spores would.
It isn't that difficult for an individual lab to produce augmented anthrax spores in small amounts - it is a "facultative anaerobe," meaning that only a tiny amount of oxygen in an otherwise oxygenless environment is necessary to induce sporulation in the bacterium. Ramping this up to industrial amounts is NOT easy, thankfully, due to the highly specific environmental conditions. Nearly any university-level lab could do the former; mostly only those at the national-asset level could do the latter. Hussein's people certainly could.