Well "similar" might be possible still within the bounds of the argument they're looking at as in a bit bigger than ATACMS, some existing missile Ukraine has made more accurate possibly.
But more to the point, forget analysing the blasts, if it were a missile strike then hitting the train and disabling the railway bridge too was very lucky, a nice coincidence!
Seems more like that was intentional as the railway bridge is the higher value target so in that case: truck or drone boat seem more likely.
I'm kinda persuaded by something along the lines of a big fertilizer bomb assembled in Russia and remotely detonated.
Little about it makes sense to me - truck bomb or boat bomb seems the most obvious, can also produce the kind of explosion seen, but one big enough, unless we are seriously underestimating the lacking construction quality of the bridge, to cause the collapse seen should have left a much messier scene and more obvious blast damage on the 2nd span and rail span. Many other types of improvised explosion should have produced a lot of black smoke - though maybe the strong and constant wind currents over the bridge are changing some factor.
It is almost certainly not a normal cruise missile strike.
FAE fits the second half of the explosion (especially if it wasn't quite optimal ratios), size of explosion vs general blast energy and the intense heat damage seen but there is little evidence of the initial fuel cloud/shockwave.
Doesn't really seem right for shaped charges - though they could have left the scene with relatively neat damage like it is and can produce some secondary venting the explosion seems far too large for that.
Then there is the train stopped so neatly there - if it had been travelling at normal speed when hit it should have continued quite some distance before coming to a stop and there doesn't seem to be anything which would have compromised it if it had been on approach when the explosion happened and subsequently stopped there - possible for some reason they regularly happen to slow or stop there though it seems unlikely, or the train driver was either in on it or train had been hijacked or something though.
Everything seems to have a bit of theatrics about it like it was staged somehow.