At KidsHealth.org, growth spurts are listed as a reason for increase in sleep patterns.
Most infants, when going through a growth spurt (usually around the ages of 7-10 days, 2-3 weeks, 4-6 weeks, 3 months, and 4 months), will nurse or want a bottle more often, and may even sleep less throughout the day. But most babies will sleep noticeably more (overall) during these growth periods because of the intense need to conserve energy.
However, Dr. Sears explains how excessive sleep can deprive a child of what is needed to thrive.
But it's possible for excessive sleep to keep an infant from thriving. "Thriving" means more than just getting bigger, it means that your baby is developing to his fullest potential; physically, mentally, and emotionally.
Babies are born with attachment-promoting behaviors (e.g. crying) that cue their caregivers to the quantity and quality of touch and feeding they need in order to thrive. Infants who sleep too much may not initiate interaction, so you have to do it (as you've been doing when you wake him up to feed).
We suggest that you continue to schedule your baby's feedings at least every three hours during the day, but let him wake you at night. Be sure to have him weighed frequently by your doctor to be sure he is gaining enough weight . Because they are not demanding babies, heavy sleepers often do not get enough to eat. This is why you are wise to take charge of the feeding routine and continue to awaken your baby for meals every three hours during the day.
In addition to insuring that your baby gets adequate food, it's also important to make sure he gets enough touch. Demanding babies often cry if somebody doesn't hold them, but easy babies often sleep right through potential holding times. One way to address this is to wear your baby around the house in a baby sling at least a couple hours a day to provide touch and stimulation.
I believe that his concerns are valid and are worth considering. Otherwise, enjoy your easy keeper!