2. This could could an attempt by a US enemy
This is possible. It could be an attempt to sow discord, or it could be a test run to see how effectively communication systems can be knocked offline.
The RV was
parked in front of the AT&T building. As you noted, the RV warned people in the area well in advance of the pending explosion, and the explosion occurred at a time and place that would likely result in few casualties. If there are no casualties, there would not be as much public support for military action against whoever was responsible versus if there were many deaths.
3. This could be the opening salvos of some terrorist group. By doing it this way, you can multiply the efficiency of all of your future attacks, since you can put loudspeakers on a vehicle very cheaply, and if only 1% of them actually explode, this is enough to cause widespread terror and disruption in potentially hundreds of cities.
This is possible, and is along the lines of what I thought when I heard about the explosion earlier today before I learned the RV was parked in front of the AT&T building. This particular attack caused fairly little disruption prior to the explosion, and plenty of time was given for people to evacuate to safety. The facts indicate care was taken to minimize the cost to citizens of the area.
5. You never know, but:
b) A bunch of big, terrifying attacks could conceivably be used by Trump as part of a coup to stay in power.
You never know, but I guess this is possible. I think there are too many institutions that have spent 4 years "resisting" Trump for him to be able to realistically stay in office. The Trump administration has had way too many leaks for anyone to even consider trying this, IMO. I also don't see the benefit to Trump in staying in power illegitimately. Trump is already a multibillionaire, has considerable influence over the country, and is unlikely to be at risk of jail when he leaves office.
c) While there have been a few true false flag attacks by the US government in the past, they're incredibly rare,
If this was the case, maybe there is a group within the 'deep state' that wants to go to war with Iran. A false flag attack to start a war with China or Russia sounds too crazy to me.
More info will presumably come up as time goes on; right now, everything is very preliminary. I'd find it pretty unbelievable if there is no surveillance camera footage of the RV being put into position, for example. Surveillance cameras are so ubiquitous nowadays that it should probably be possible to trace the path of the RV at least to the edge of the city, though it will take a lot of time to collect all of the footage.
Today, it is very common (and sometimes even required) for people to be wearing facemasks in public. Whoever was driving the RV could have had a facemask on while driving, got out of the RV with a facemask on, and walked to a residential area without security cameras, where he was picked up by an Uber some number of hours later.
Edit to add:
I don't think this is an anti-5g group. 5g towers only
reach about 1500 feet, so the impact to 5g specifically would have been low.