No. While it is "possible" it is certainly not "plausible." Please explain why if you were trying to divert attention away from a stolen good such as fertilizer you would engage in a criminal act on such a scale as to get the world to focus on the very thing you would like to draw attention away from?
Look I don't believe in this theory. But the part you are missing is the "And maybe the explosion turned out much larger than the thieves expected..."
You look at the explosion see how big it was and say "nobody would be willingly cause that big of a problem to hide a smaller crime." But when you think that you are thinking backwards. You know how big the explosion was, therefore you conclude whoever did it must have known how big the explosion will be. That's not really correct. They might have underestimated for technical reasons, they might have underestimated because they are incompetent.
It is kind of like asking "who would burn down 22,744 acres for a gender reveal party?" Nobody intentionally, that's for sure. But the Earth is full of stupid and/or incompetent people.
If you felt your theft would be discovered, you could very easily expect the explosion would destroy all traces of the theft and nobody would know any better. Many people, especially uneducated people, would not have expected that the theft would be detectable by the size of the explosion. I'm pretty smart and well educated, but I'm not even sure such a thing would have occurred to me, and even if it did I might have preferred my odds taking my chances on that anyway. To be very clear though, I wouldn't have done something so heinous in the first place.
Given the sequence events, with the welding going on etc, I don't think this happened. But not for the reasoning you gave.
