Didn't click the link, but maybe acrylic. My 210 AllGlass weighed more than that.
edit* I put it my info for my 210, and it came up with this. Seems right.
Material................................Glass
Tank Overhead Shape.....................Rectangular
Length..................................72.00 in.
Width...................................24.00 in.
Height..................................29.00 in.
Wall-thickness..........................0.50 in.
Volume..................................216.94 gal (US)
Tank Material Weight....................349.94 lbf