Delilah, I am so sorry you had to go through a tantrum, as I've been there many times myself (though not yet with my daughter as she's only 8 months old, but with nieces/nephews). I'm sure you did what you thought was right, and I can't say I would have done anything differently either.
When posters like lc1965 say that you should have waited for you child's tantrum to end before boarding the bus, I really get annoyed. First of all, had you waited, I'm sure you would have gotten comments about how sitting at the bus stop with your screaming child annoyed/disturbed the others at the bus stop. So either way you can't win. Also, how are you to know how long the tantrum will last? With kids, those things are so unpredictable, it could have been 2 minutes or 20 minutes. You said he didn't calm down till after you were in the room-so I'm guessing that was at least 20 minutes from when the tantrum started, based on walking to the bus stop, waiting for your bus, the bus ride, plus walking from the resort stop to your room. It might have even been as long as 45 minutes, who knows, but had you just sat at that stop for all that time, wouldn't you have been doing a disservice to the others at the bus stop, and at DTD all the stops are close enough that everyone waiting would have been 'inconvenienced'. Then you would have been written up as the terrible mom who let her kid throw a tantrum at the bus stop.
Should you have taken him out of the Hall of Presidents? Not in my opinion. You said he wasn't crying or being loud. Well what do others expect, total silence? It's not an R rated movie, where you wouldn't expect to see kids (not getting into if there are kids in there making noise), it's WDW where kids are welcome in every attraction. Kids talk/laugh/make noise in every attraction in WDW, so do adults, so should they all be removed? My daughter went to the Hall of Presidents when she was 3 months old and it was her favorite attraction the whole trip. It was the first time she laughed, ever in her life, not just on the trip. Yes, she was laughing and squealing in excitement at these plastic men talking and moving around. Did it disturb others? Possibly so. But she was happy and loved the show so I didn't even consider leaving. We saw it 2 more times on that trip and she loved it each time. I don't think her enjoyment should be compromised anymore than an adult's should be a child. if only one person was bothered by the child's behavior, then it couldn't have been too bad.
Kids aren't quiet creatures by nature. We can try our best to keep them quiet (and I do, though it's easy now cause my daughter is an infant), but sometimes it's not possible. To say someone shouldn't take their child back to the room, but rather wait and let them keep screaming at a bus stop is ridiculous. How is that beneficial to the child. If the child is acting up like that, odds are they need a break/rest, so even if it means they cry on route to that rest, sometimes it's the only option. Keeping the child out, simply so people on the bus get a quiet ride isn't really in the best interest of the child.
So again, Delilah, I think you did a great job with your child, and I agree, parents don't always know what the best solution is at the time they need to decide. What works one time may not work the next, and you only find out through trial and error.