um... looks like you've got pecs there.
if you're missing muscles, there is a BIG problem, and your activity would be greatly restricted. i'm guessing you misunderstood the physician, especially since you say it was "a few years ago".
now, as for your friend being able to lift more than you:
your muscles are under-developed. don't feel bad about it, we all start out somewhere. that said, your friend can't be that much smaller than you, and in all probability he is a bit bigger than you. even at that, you can't say your friend lifts more than you when it's only 5 or 10 lbs. some weeks my bench goes down 5-10 lbs. if i didn't get enough sleep, food, etc.
if your friend IS in fact smaller than you, is he shorter than you? short people typically can lift greater amounts than tall people (it's all physics). the bottom line, is if your forearm is 3 feet long, it's a lot more difficult to curl 90 lbs than it is if your forearm is 1 foot long. it has to do with lever-arms.
if you're looking to put mass on, look around here, it's a great place to get started. i wish i had found this site when i first started lifting. there are so many basic things about nutrition, routine, exercise form/execution, etc. that would've helped out so much if i had taken the time to learn them when i first started.
good luck, and keep learning.