I am also not an expert, but I believe AN is not really explosive by itself. It needs to be mixed with Fuel Oil to make an ANFO explosion. Plus, you need a detonator. A simple warehouse filled with fertilizer doesn’t do what the Beirut site did.
I believe the freighter in Texas City in 1947 was carrying just ammonium nitrate when it caught fire and blew up.
I would refer everyone to the Texas City explosion in 1947. Three ships loaded with AN caught on fire and exploded. It can happen.
You’re mistaken about AN being hard to set off. All it needs is to get hot enough. Check out the Texas City Disaster.
https://en.wikipedia.org/wiki/Texas_City_disaster
In 1947 a French ship loaded with 2300 tons of AN caught fire and then exploded in Texas City, TX (think Galveston). This then set off another ship with almost 1000 tons of AN.
Almost 600 people were known killed with possibly hundreds more unaccounted for. Two sightseeing planes were blown out of the sky.
One of the ship’s 2 ton anchor was thrown over 1.6 miles away.
Again, AN does not need a ‘detonator’. Just get it hot enough.