Pretty much, unless it says "RailKing Scale" (these are the earlier Premier pieces, mostly diesels that no longer have today's expected add-on detail), it's less than 1:48. But: the RK USRA 0-8-0 has always been marketed as RK, yet has always been a true 1:48 model with basic, but correct, detailing. The RK USRA 0-6-0 (there is a Premier version, too - I own one) is pretty much the same kind of deal.
The RailKing Scale diesels can be big bargains - the detailing is all I require, they are very good replicas, and the cost is sometimes quite a bit lower that Premier - with the same operating system.
My RK Imperial Triplex looks like a 1:48 model of a smaller prototype - the cab is full O-scale, for example - but the actual smaller "prototype" never existed. Most RK, including Imperial, are undersized and look it, though they can look very nice. This, of course, does not apply to RK "Scale" items.
BTW - it is spelled "Premier" (which is "highest in quality"), not "Premiere" (which is the first showing of a film or the like).