Carpets cleaned by shampoo (most of which have always been, Crystallizing) will re-soil quickly if the crystals are not thoroughly vacuumed out of the carpet when dry. The crystals contain the soil, and gets released in a short time as the crystals break down. Mike has however already vacuumed most of the foam and soil away and as the last foam layer was applied onto a cleaner carpet the captured soil would be less in any case, so re-soiling may not be an issue.
My first carpet cleaning machine nearly 30 years ago was a Von Shrader Carpet Deterger. The vacuum system was a waste of time, as it only collected a minute amount of black slurry, when doing a full lounge. The vacuum orifice was far too wide for a small single vac motor and although the carpets looked markedly better afterward s (Thats what shampoo's do with their abundance of optical brighteners) they did re-soil quickly.
Dave.