Trub in the fermenter isn't only yeasts that have dropped out of suspension. It also contains proteins and hop debris transferred from the kettle, which can vary considerably depending on several factors. Probably the biggest factor is how well the proteins were allowed to settle out before transferring from the kettle. Generally speaking, higher gravity beers will have a proportionately larger amount of kettle trub, Lesser factors include protein content of malts, adjuncts and/or extracts.
Healthy yeasts will multiply in order to meet the demands of fermentation. The demands vary but, as a rule, higher gravity beers have a proportionately greater demand. It's more complex than that, but a subject for another thread. Both yeasts and proteins will settle out and compact in the bottom of your fermenter given enough time. Lower temperatures will speed the process.
My guess would be that you got a much cleaner transfer of your second batch, and/or allowed the yeast and trub to settle out and compact more at the end of fermentation.