Seen this happen many times as well.

Were you wearing gloves? Disease (such as brain flu or infected wounds) can be transmitted from person to person and has a lot of variables to it which determine the likelihood of it happening; One of the things that matters is gear. It makes plenty of sense for someone with infected wounds to pass the infection to someone else that happens to be touching the wound. I don't know if you played the mod, but you could pass infection via coughing (airborne) near other players.

In my cases I've always been alone, and I've only ever gotten a sickness AFTER applying alcohol to my wounds from zombies. As my wounds get cleaner and cleaner the sickness then goes away. The sickness should be contracted (I would think) if you leave your wounds open without cleaning them or directly from the zombie, not after the cleaning of the wound.

They fixed medications making you sick.

The logic of medication effect also working on the person applying, not only the receiving person is worth checking out.

Hello Paradiz and thank you for the report.
Unfortunately we were unable to reproduce the issue you have described. Please retest on latest build and report back in case the issue re-appears.
Regards,
Geez