Seems maybe an order of magnitude off, depending on definionion of "thing." I cleaned out my mom's house after she died, and if I counted individual photo prints, 30 years worth of tax returns, canceled checks, paid bills, etc. she had a lot of "things."
tl;dr - The figure seems to come from Regina Lark, a "Professional Organizer" who "specializes in working with people with chronic disorganization, ADHD, and hoarding disorders, as well as folks who have way too much stuff," although she suggests 30,000-300,000 items. I still think 30,000 is way off, however. I'd struggle to get to 3,000.
