Scrapbook saves not only the image clip but information within the clip area that it finds to give the scrapbook entry some context, whether this is the URL that the clip came from in the case of a browser clipping or some other information. Its this contextual metadata that you're probably seeing pop up in your text messaging application when going from scrapbook to texting. This is why I don't use scrapbook on my note devices; its a proprietary software that is so limited in functionality that it serves no purpose for me since the data that I put into it is not useful to me on my computers or other non-samsung devices. It wouldn't be so bad if the images within scrapbook could be separated from the metadata but the export features are limited and when editing a scrapbook entry one is unable to share the clipped raster image individually either. I make no claims as to whether or not it is possible other than to say that if it is it's not intuitive or easy.
If your intent is to attach your clip to an SMS message why use scrapbook? Why not just use the share via menu instead and share the clip directly with the messaging application of choice?
Personally I like ES File Explorer as my main file manager application and I like the fact that ES has an entry in the share menu. What this allows me to do is to use the image clip feature of the S-Pen and then share via ES to save the clip to internal storage. I can then do whatever I wish with that file since the image is now stored and visible by file manager or gallery.