When they do an autopsy, they take blood, fluid, and tissue samples from multiple locations. In this case, they analyzed blood samples from the aorta (the large artery leaving the heart) and femoral vessels (blood vessels in the thigh). They also analyzed a tissue sample of the liver (a small piece of the organ). The units (mg/kg) are commonly used to give the concentration of a drug in the blood. This translates to milligrams of the drug in the body per kilogram of body weight.
Citalopram is an antidepressant. The concentration in the blood sample appears to be within the therapeutic range, and was probably not toxic.
Methadone is used for the treatment of pain and also some drug addictions. Toxic levels of methadone in the blood are 1 mg/kg, so the levels in the blood samples were not toxic. Methadone is stored in the liver, so you would expect to find higher concentrations there.
So, assuming that the toxic levels I just looked up on the internet are accurate, the levels of both medications at the time of death were not toxic, and thus probably didn't cause the death (assuming there's no interaction between the two drugs). Of course, there are a ton of variables to consider when determining cause of death, and toxicology is just one of those.
What you should do is contact the medical examiner's office and request a copy of the death certificate, or possibly the medical examiner's report. I'm not sure which of these documents is a matter of public record that you would have access to as a friend, or if any of these documents is only available to next of kin. But you would start with the medical examiner's (or coroner's) office where the autopsy was performed.
