That's very possible! So since my mother has retired her driving habits have gone from miles per gallon to months per gallon. Her 2010 Mazda 3 has about 65-70,000 miles on it.I'm going to speculate that short trips by the previous owner, and 5 k changes, led to moisture and some sludge. The OP with a better regimine has cleaned the sludge to some degree and its evident on the pickup screen.
Even with decent oils, lots of short trips without full warm ups lead to sludge.