I'm not making an assumption on anything. I'm just saying that the odds are that if the other bearings are set up fine, than the one that went bad was probably fine when it was packed and installed, especially if the bearing on the same side is checked. If two people do the work, they usually each take one side. What I wouldn't assume is that the bearing quality was 100% fine. Bearing do go bad. Cheap bearings go bad more often. I have no idea what brand bearing that they use. If it were mine, I would check the existing bearings on the old axle to find out what brand they are.
If the OP wants to save some money, he could put new Timken (or other quality bearing) on the old axle and run it for a while. I like to match axles, but in the short term it won't hurt anything on leaf springs with an equalizer. I wouldn't do that with a set of rubber torsion axles.