Einstein's train thought experiment

I know similar questions have been asked multiple times, hence I'll get straight to my doubt which I couldn't find cleared in the other ones.

The earth frame observer sees the lightning flashes simultaneously and he sees that the person in the middle of the train would receive the flash from the ahead one before the rear one. Now the thought experiment continues by saying that the observer on the train would also see the ahead one before the rear one and hence conclude that the ahead flash occured first.

My question is why is it being assumed that the earth frame observer seeing that the ahead flash hits the observer in the train first imply that the train observer would also see the ahead flash first.

• Suppose the first flash knocks the train passenger to the floor, causing the second flash to pass completely over him. Surely both observers must agree on that sequence of events. Dec 18, 2020 at 19:28
• What if when the observer was centered between the two flashes His train was moving east as the earth rotated At 1000MPH? As well as orbiting the sun at 67,000 mph as it rotated around the galaxy at 490,000 MPH. Add to that 3,600,000 mph rushing toward other galaxies. If they all lineup the observer could be moving over 4,000,000 miles per hour. Would that make a difference? Dec 18, 2020 at 23:24