Unfortunately the "BioBricks" website does not list any weights. However, the following link is helpful and probably accurate enough to straighten the delivery guys out, although the numbers may be off a little bit.
Online Retailer’s (“Dirt Works”) price list, for BioBricks, with notations on weight
http://www.dirtworks.net/Buy-Good-Firewood.html
1 Bundle / 20 Bio-Bricks = 39 lbs (* this number may be wrong)
1 pallet / 50 Bundles; 50 @ 39 = 1950 (50 Lbs under 1 “short” ton / 2000 Lbs)
*Note, I have actually seen a 20 Brick bundle of BioBricks, my memory is that they actually weigh 38 LBs, in which case a 50 bundle pallet would weigh 1900 Lbs, which would be 100 Lbs under an official “short” ton. That would seem to allow 100 Lbs for the weight of the pallet and any packaging materials (essentially this is just the shrink wrap on the individual bundles and the whole pallet itself).
Also note, a “long” ton is 2240. This is a traditional unit of measurement in shipping. Unless the average pallet weighs 240 Lbs, that wouldn’t seem to have any relevance here.
The real question is how much would the bricks themselves (1900 – 1950 Lbs) plus the pallet weigh. As long as the total is under the truck's capacity you should be ok.
Based on the above I have no idea where they are getting 2400 Lbs, unless they misspoke or you misheard them and the number was actually 2240 Lbs. In any case, for the reasons outlined above, that number doesn't apply.
~Cath
