The basic Uranium enrinchment process goes like this:
1) Uranium yellow cake (U3O8) goes through several chemical process to convert it into Uranium Hexafluoride (UF6).
2) UF6 has an interesting phase diagram -- it has a triple-point at roughly 64 C, and 1.5 atm (22 psi). So you don't have to heat it up very much to make it sublime into a gas. You can then feed it into a cascade arrangement of gas centrifuges.
3) The gas centrifuges take advantage of the fact that there's only a single natural isotope of Fluorine on earth, and therefore that the UF6 molecules will vary in molecular weight based only on the isotope of Uranium they contain. Through centrifugal action and a slight thermal gradient, they can separate the UF6 that contains U-235 from that containing U-238.
The problem with MoF6 is that it's denser than UF6 and therefore has a slightly different phase diagram. At the operating temperature/pressure of the gas centrifuges, MoF6 will condense into a liquid, which the gas centrifuges aren't equipped to handle. Moreover, because of the cascade arrangement, one centrifuge failing can spew unexpected matter into downstream centrifuges, causing
them to fail, etc.
I don't know whether the blogger was being literal when he said it "destroyed" their centrifuges, but it's certainly possible. The gas centrifuges used in Uranium enrichment are vacuum sealed and operate at 500-600 m/s, depending on your metallurgical skill (i.e. nearly Mach-2). Higher operating speeds are more energy efficient and, more importantly (if I'm not mistaken), also result in a higher yield of U-235. If Iran is already pushing the limits of their metallurgy* to maintain higher speeds, then it might be possible that injecting too much dense matter (i.e. MoF6) could over-stress the centrifuges and make them literally tear themselves apart.
Is this the work of Stuxnet as the blogger speculates? Eh...I don't know. Iran
claims to have been producing their own UF6 since back in, like, 2005. But it's a dubious claim, and it seems more likely that they were just buying UF6 from Pakistan. In reality, they were probably hung up at the UF4 stage until relatively recently. But if I understand the process correctly (and maybe I don't), Mo and other impurities arise in the U3O8 -> ... -> UF4 process, which Iran probably
has been playing around with since 2005-2006-ish. In which case, the MoF6 problems probably aren't the work of Stuxnet, at least not exclusively. Any way you turn it, though, I doubt it's helped.
* Edit: and by "their" metallurgy, I probably mean Pakistan. No one can prove it, but Iran's centrifuge design is suspiciously similar to Pakistan's. You can thank
this guy for that.