Quarantine

Both Sleeper and Talocan sites make reference to a large effort to quarantine objects. The logical conclusion is that both races were attacked by a highly deadly virus.

The Talocan show no signs of an infomorph society. Therefore there were either two really deadly viruses in the same area of space, or the Mirror's medical enclave refers to treating biological people.

Was the virus manufactured? A highly parasitic organism such as a virus doesn't usually evolve away from the host.All known races that have visited Anoikis have entered from New Eden, making it possible that it was an offshoot of a New Eden virus. That it evolved separate from the host is very low probability. However, it is within probability that the Sleepers had the ability to create such viruses.

For a digital virus to create itself it would require self-improving AI, potentially within the reaches of the Sleepers. There is no concrete evidence that they ever achieved sentient AI though. Both races would be able to create one without doubt, the question is whether they would be able to create one that ran on the other faction's hardware.

In summary there are two high-probability cases: The two races engaged in viral warfare. If one virus was created, it was biological and it turned on the creator, the Sleepers were also biological. If two were created, then the Sleepers could be infomorphs and one virus was digital.

The virus was brought in and it attacked both races. It was biological in nature, the Sleepers were also biological.