This just happened to me and I've been trying to find an answer online to no avail.
My son started crying a little bit ago, so we started to heat up a bottle. Both my wife and I had to use the master restroom for a moment, and by the time we were done and the bottle was ready, our son was back asleep.
I wasn't sure though if we should have woken him up again to take his feeding and diaper changing, or if letting him continue to sleep was the right thing to do.
He is 3 and a half months old, and we think he is either going through a growth spurt or starting his first tooth, so the wakeup may have been related to either growing pain instead of hunger, but we're still not sure if we should have picked him up and tried to feed him anyway - should we have?