Twin brands, like Roo/Shamrock, are very common in the RV Industry. Even sacred Winnebago does it.
As was stated, it's so two dealers can sell them without impacting each other's brand rights.
That's why the salesman will diss the twin brand and tell you lies in order to sell you the trailer.
They are both made in the same factory, on the same assembly line. No difference between them except for outside decals and interior decor.
The salesman was feeding you total BS.
If it were me, I'd report him to the owner or manager of the stealership.