I have some thoughts and also some questions. First of all, can someone confirm that Noel's last sighting was at 14:56? Another user said that but I haven't found another source for that info. I agree this would be a sign that he took the train to SF, but even without this info I'm convinced that was his method of transportation for multiple reasons. At the time, the Overland Route went right through Reno and ended in SF, which was his destination, it would make most sense for him to take the train. Taking a quick look at Newspapers.com, this route is mentioned quite often in Reno newspapers, this strengthens my belief he did take the train as this route seems to have been very well-known/popular, but if someone more invested in train-history thinks this is wrong then please correct me. But if he did take the train, this leaves me more confused - because how did he never make it to Irene (his sister)? Trains are a very straight-forward method of transportation, you get on, go to your destination, and get off.
Another thing I've been wondering about is when he was reported missing, I couldn't find an article about his disappearance in Newspapers.com. I searched both his name and his parents' names, and as mentioned by others, in their obituaries he's listed as a survivor. Who reported him missing and when? I imagine it's possible articles might have existed but have gotten lost through the years, but it's still weird I couldn't find a single one.
Below is a picture of the Overland Route from 1908, taken from Wikipedia. If the route looked the same at the time of Noel's disappearance, the remaining stops for the train - except SF - would've been Truckee, Sacramento and Oakland; possibly also Marysville and Port Costa, but I'm unsure as this map is confusing and honestly gives me a headache. All of these stops are within California. He might've gotten off at the wrong stop, but if he took the Overland I don't see how he would've gotten off at the wrong place as SF is literally the final stop, but we all have weird brain-moments. He could've made it to SF and something happened when he got there. Then there's the possibility of voluntary disappearance, maybe he got off at the wrong stop on purpose to start a new life?
It's also not mentioned if he was supposed to go to his sister's and brother-in-law's adress himself or if they were supposed to meet at the train-station. If they were supposed to meet when he got off the train we can be sure he was never in SF, but if he was supposed to go to their home himself he could've spent some time there.