I know exactly what you mean, and I think it is part of the "Boden kitsch" the company creates. When mixing patterns, you want to look at elements such as color, scale of pattern, pattern design, etc. Sometimes I think Boden stylists purposefully ignore any of this analysis and just stick random things together, market it as kitschy and Boden-esque, and somehow all the pieces magically sell out.
You ever notice how whatever colorway featured in the Boden catalog sells before the other 3-5 colorways? Boden patterns and styles are very distinctive, and I think their clothes live and die based on those suggestions on how to style.