Dana there are no 'current' Burros, they are no longer made though the last company to make them kept their web site up, which is a nice resource but sometimes confusing as Burros were made in three different places over many decades.
The ad does not give the year but the look of it tells me it is likely an older Sac City Burro, made in Sac City Iowa. When the Burro resurfaced in CA there were several changes to the 13', the door was made less curved, refrigerators replaced the ice boxes, etc. Not sure of all the changes, but it is possible changes made increased the weight
. We just sold our Sac City Burro and yes the tow weight is about 900#, very light
and very maneuverable, a good trailer for pulling with a small tow vehicle.
I notice the one for sale does not have a cover over the front window, which actually was an 'option' when new but don't know why someone wouldn't want it. I would suggest anyone buying this trying to find a way to make or have made a cover, there are posts on the forum of the pros and cons of covers but in my book keeping out rocks, water, etc. when towing is essential. This trailer looks in very good original shape.
Folks usually list the weight given by the manufacturer at time of sale, but if there are any options added (I notice a vent fan) that adds weight. As mentioned on the forum in many places, many manufacturers tend to give low weights for the most basic model.