Timing changed after Cap + rotor swap?!

The reluctor/pickup or points, etc determine firing of coil. The cap and rotor are along for the ride.

The mechanical advance could have been stuck in a slightly advanced position when static, now with dinking around, it's snapped all the way back to where it should have been resting. That vac adv one is an interesting deal.

Re-time the engine, check total and move on if everything is OK.