Do you have a reference for that? In most contexts, even very high levels of CO2 up to 5% have been shown to protect animals and people from seizures.
5% CO₂ inhalation suppresses hyperventilation-induced absence seizures in children. - PubMed - NCBI
5% CO2 is a potent, fast acting inhalation anticonvulsant
Stopping Seizures With Carbon Dioxide
Yes, CO2 is usually protective against seizures but in some people it can induce violent panic attacks. Severe panic attacks can trigger seizures. In people with epilepsy it may also sometimes have paradoxical effects. This is similar to the gas nitrous oxide (not the same as NO) which is also usually calming and used for anesthesia. It can also trigger seizures in some people. Demi Moore is the most famous recent case who had seizure as a result of nitrous oxide. But she was abusing it and like I said before, if it is indeed CO2 that triggered a seizure the person is probably breathing a lot more than 5% and for very long time. In other words abusing it to the point of loss of consciousness and acidosis.
There cases are rare, and I am not saying this is what happened or the norm. Just trying to come up with an explanation that involves CO2. Chance are it was not CO2 that triggered it.
Abnormal ventilatory response to CO2 in epilepsy patients: a potential biomarker for seizure induced respiratory depression & modification by SSRI | Grants Awarded | Our Research | CURE Epilepsy