I can believe that. Rather than distinguishing between MMW and x-rays, assuming that passengers (and TSA) get confused about which is which, they say that patients should avoid scanners.

This, for example, indicates that one manufacturer didn't go too deeply into their research:

"Medtronic has conducted official testing on the effects of the new full body scanners at airports with Medtronic medical devices and have found that some scanners may include x-ray. "

IOW, "abundance of caution."

As I think people should opt out anyway, for a myriad of other reasons, I absolutely support the right of people with insulin pumps opt out because of the manufacturers' caution.
The article says it was an x-ray based scanner, not MMW, and that the manufacturers had warned about x-ray scanners affecting the software. And even there, it appears that the manufacturers have made a blanket statement about any x-ray device, including the scanners, rather than investigating the scanners specifically. (To be honest, the article doesn't even confirm whether the device actually malfunctioned or not.)

As above, there are a lot of reasons for opting out, and with the x-ray scanner, I would include possible health risks for EVERYONE, so this is emphatically not a defense of either kind of scanner. But I don't think there is evidence that "MMW scanners have damaged insulin pumps."