Yeah it happens :-/
Okay so I just want to give you some pictures for reference ^_^
(not my picture) but here is a boy who is well fed, most likely fed on a diet of live foods. But you can see his stomach behind his gills is very full and he looks healthy. (Top picture he's flaring his beard out so that's that yellow and black thing)
And one of my boy's; Jarvis, he's got constipation issues and will only poop once a week but is otherwise healthy. You can see her he's got quite the stomach s well but it's still not what I'd consider bloating or anything, just well fed. Now if I knew that he hadn't eaten in a week and still looked like this, then yeah I'd be worried but this was right after a meal.
And one of my former girls who was Eggy at the time, so she looks rather bloated and I thought she might have been until she dropped her eggs the next morning and went very skinny lol.
And this was one of my girls who passed due to Dropsy which is an organ failure. So either her kidney's or her liver failed and stopped processing the fluid and so she began to retain the fluids which leads to pineconing as you can see; it's the scales becoming raised as the Betta swells and then eventually death. I don't mean to scare you or anything! This doesn't just happen all the time!!! This is my first fish to die of Dropsy so no worries about it effecting your fish!
She was a big girl anyway, she was Plakat so shorter fins with a bigger, thicker body. So I didn't catch Dropsy in time and sometimes you can catch it early enough and reverse the effects depending on what fails and when you catch it. But she died the next day even with treatment, but she's in a better place now
And this last picture I attached is the sort of Bloat you'd want to watch out for, this poor boy definitely has it bad. So your boy is just well fed is all, sometimes it takes them longer to process food depending on their health status so a little bulge is to be expected