The ruling from the original court was that Trump engaged in an insurrection (but enjoys presidential immunity). The presidential immunity bit was then appealed to the Colorado supreme court, who overturned that. That is how we have arrived at (a) he was in an insurrection and (b) he does not qualify to be on the ballot. Trump and is team have never contested (a), so as far as this case goes there is no question about whether he engaged in the insurrection.