Hi P.,
I would have to say that yep, unfortunately they are a normal thing at this age. My DD, turned 4 in March who never went through a terrible two phase now pitches a fit over any little thing, same as your DS right around dinner, very picky eater as well. We don't give in, we ignore or if she gets too out of hand a simple threat of time out will usually chill her out.
Our DS, now 13 was the same way at 4 from what we remember. although he had all the terrible two's, trying three's, and then moved into the moody four's. My sister, who has 8 kids will tell you as well that at 4 kids will throw fits and test you. They are at a strange age, they want to grow up and they want to be your baby at the same time. They are conflicted and get mad and any little thing can set them off, ergo "moody".
We are really working with a DD on her fits because she is starting Kindergarten this month and we've told her that her teacher won't put up with tantrums and all this nonsense or she'll go see the princepal and that is not a good thing.
The good news is that it does go away by the time they're 5. Our daughter is going to Kindergarten early because she passed all the test and is bored at home and I've gone through every workbook with her sold in the stores so hopefully school will have a positive affect on her. Our DS outgrew them by the time he entered Kindergarten at 5.
Hang in there, it will get better. Just see it from his perspective and you'll have a better understanding of why he flies off the handle so often.