Constipated?

My 6 month old son just had a "different" diaper.  I already called the pediatrician but I don't feel terribly informed, so I am asking you ladies....

He had blobs (for lack of a better word) of clumped poop with regular poop.  Is this constipation?  I thought that ALL of it would be hard if a baby is constipated.  He did have banana for the first time yeaterday, but is was thoroughly pureed.  Maybe that did it?

Anyone have any ideas, experience or advice?  Thanks.