As an introvert myself, I don't think it's easy to just declare this 'introvert behavior'. Mainly because more of these actions you describe sound like controlling behavior, period. Playing a game with other kids.... are they all in the same room, or meeting up online? My nephew is very introverted (we have the same Briggs Meyers results) and will play video games online with a group, but get him IN a group of other kids and he's far more reserved. I myself tend to avoid 'big group' things (like a "mom's brunch" with mom's group) but am fine at a sports event with just my husband or another couple, or sitting with a couple of ladies to enjoy a drink in the evening. It's really about the level of intensity of the situation. I enjoy more intense socializing with just a few people far more than small talk with 'the group'. The small, intense socializing is energizing to me, while a group event is decidedly draining.
People aren't static, and there are various degrees of introversion. From what you write, it doesn't seem so much a problem with 'introversion' inasmuch as you have a problem transitioning an unwilling kid.
Some kids who are anxious about something may show these sorts of actions. I've seen it on a few occasions with children who had a big change coming up (starting K, new baby, other big events like moving houses).... when I was a nanny to those kids, I realized this was largely about control. They couldn't control other areas of life, but pitch a fit! and see if they couldn't get mom to say "heck, we'll just stay home!" It can get ugly, but if the end goal is having control, they got what they wanted. I have a sister who has had spells of agoraphobia+ OCD and a sense of control is often at the crux of it. Leave the house and that control is GONE.
I've taken care of a few strongly introverted children and I didn't see their introversion manifested in the ways you describe. Instead, the child often had a strong sense of how they cared for themselves and would bring books/an activity to focus on (instead of the other kids) or was very talkative and relational with one or two close friends or the adult. How it manifested was that the child usually didn't go off with the group of kids there, but would find themselves quite comfortable just doing what they wanted to do. As a kid, I would end up going on walks alone; was always a solitary kid, liked having that quiet time. I didn't fight about going out, though.
I think, instead of focusing solely on the introversion, it would be good to help your son get *out of the habit* of stalling and gumming up the works when you are ready to go. You might need to create a light incentive program, something which suits him. (maybe after 10 times of leaving the house with no complaining, he can pick out a family movie for a fun popcorn and snuggles night, or beg off running an errand when the other parent is home?) When my son (7) starts to fuss about having to go to the store, I might offer that he can ride his bike, or put a small carrot out there--- we can watch a show after we get back, etc. I can time privileges like tv/video games to happen AFTER the errands which need doing. Small carrots, but it gets him out of the habit of arguing.
I also might just get myself ready, grab a book, and sit on the porch and wait until he's ready to go. Immediately, I've removed the attention (me).... I think the trick though is that you have to allow extra time for the transition. And then, don't get hooked in emotionally; stay neutral as much as possible around this.
The book "Taking Charge: Caring Discipline that works at Home and at School"by Joanne Nordling also has some good approaches, too.