Brakes have already been mentioned but I'll provide some specifics. Most road bikes are marketed as "go fast" bikes and until recently used skinny tires and short reach caliper rim brakes. These brakes when measured from the center of their mounting post to the center of their brakes pads would in the 40 to 50mm range. Touring bikes were designed to use fatter tires that requires different brakes - often cantilever or V brakes. These provide more tire space. Sport Touring bikes are similar to a touring bike except maybe lighter tubing (because it isn't going to carry as heavy a load). If it uses caliper rim brakes, they had more clearance under the brakes and their reach would be in the 47 to 57mm range. Just in case it isn't obvious, the frame determines which kind of brakes can be used and one type can't be exchanged for another. If you are getting a touring or sport touring frame, what you don't want is one with 39/49mm brake reach.

On a touring bike the cyclist position tends to be more upright. Their handlebar height might be about the same as their saddle They are looking around instead of being more aerodynamic and perhaps drafting the bike in front. This higher handlebar position probably requires a larger frame. If I was looking for a vintage sport touring bicycle for myself that uses a quill stem, I would want one as big as I could straddle the top tube comfortably. There are exceptions but many common quill stems did not allow for them to be raised very high up. They were made for racing bikes where the handlebars might be 5 or more cm lower than the saddle.