At 14 and presumably back at school this week/next, yes, he is overweight, but he's about to do the 14 year old boy thing of sprouting several inches in a very short time whilst having fewer opportunities to eat crap (because he's in lessons), more activity and more of a routine.
So, if things remain the same in food, there is a very good chance that he'll stretch out to around a 32-34" waist with no noticeable effort.
To give an example, I'm a fat bastard. I put weight on in lockdown on 1600 kcals a day, much to my disgust, but I was ill, I didn't leave the house, I couldn't move for gasping for breath. I had to buy new trousers and a couple of tops to be able to go back to work, 1-2 sizes larger than I was wearing in March.
I've worked for ten days, five hours a day, over the last 28. Hardly an Olympic level effort. Those new clothes are already hanging off my waist. I haven't changed what I've eaten, I haven't got taller, but I have been moving for the first time since the end of March.
It's very possible that your SS will get slimmer just from being back at school - and lots of them will be conscious that they've put on weight, the staff will be conscious of the plummeting levels of activity and fitness and PE will be planning ways to get all kids fitter and slimmer without embarrassing them or drawing attention to the weight gains.
I'd say hold your own counsel. Because things are very different this year and putting pressure on never works. Hopefully, it will begin to resolve itself and if it doesn't, well all you should do is provide good quality meals when you cook - in appropriate portions for the eating machines that are teenage boys in the growth spurt that takes many of them to over six foot, not for teeny tiny women in their thirties and forties - and leave it to him, not his parents, to deal with.