haha about no 3 bananas! 
I don't think you have it wrong, you know him very well and of course he needs to run around and be stimulated!
one thing I learnt from Tracy Hogg's books is to always "step back" and just observe the behaviour - I sometimes pretend it is not my child to reduce influence of my enotions on how I see the behaviour and how I react - if that makes sense
my now 9 year old DS2 threw his first full blown tantrum around the age of 2 - he was rolling on the floor howling, screaming, snot bubbling, mouth frothing to my absolute bewilderment!
I had to give him a "cold shower" (lukewarm water) to shock him enough to stop his overreaction - I can't even remember what it was all about, I know it was lunchtime so perhaps I wanted to clean his hands or put him down for a nap or some similarly vile & bossy thing!
he still has tantrums and is bloody stubborn, at times he would rather put his head through a brick wall then do as he is told!
so if he your DS is a strong willed child you better strap yourself in for the rocky ride ahead - he will want to be in control and do what he wants at all costs!
I agree with pp, he is definitely trying to change the dynamic and seeing how far he can push you, what he can get away.
One thing tends to work well is to let them make decisions in small matters such as which top he wants to wear or what he prefers for dinner - but only ever give 2 choices.
this way he will feel a bit more in control and might listen to you better in other things that he can't choose.
you must carry on being firm and try to be patient (soooo hard!), but you've got the loving thing right already, so I'm sure you'll find ways to teach and reassure him at the same time!