The little guy is really making progress in his physical development! Not only is he moving extra quickly (and sometimes mischievously) when he is crawling, but now he is in the earliest stages of standing on his own.
Basically it does not happen by him saying to himself “ok, I want to stand without help.” What happens is that he does his usual, where he pulls himself up into standing position using something like a sofa. Then, what makes it interesting now is that he will get focused on something he is holding (either that he stood up holding or grabbed onto while holding), and and he will forget for a few seconds that he is standing. So, he will just stand there, suspended, either looking at the item or deciding if he should chew on it. Then, just as quickly as it happened, it is over, and he is back on the floor crawling around.
Soon enough it will become more and more regular, and more stable, and will last longer – and then of course comes the big one: walking!