A previous poster, who is only an inch shorter, described herself as "quite a bit overweight" despite being a size 10.
That was me. When I was last wearing size 10 jeans, my BMI was 27-28. Before that I had been wearing size 12 jeans, which were getting tight but still fitting and I was most likely obese. (I didn't weigh myself until I'd lost weight and when I did my BMI was 29.5, so presumably I had been obese.) When my BMI was 26.5 I could fit into 15 year old size 10 jeans or modern size 8. Up until March of this year, I had a BMI of 22 and was wearing size 4 jeans from Primark. I've been unwell since then and am on medication linked to weight gain, so am now wearing size 6 jeans, which sounds tiny but my BMI is 24.5.
Vanity sizing is real. For all of my late teens, 20s and early 30s, I was a size 10. I was slowly gaining weight through that time and the size 10 I wore at 18 would absolutely not have fit me at 32. But when I bought new jeans, I always bought a 10. In that time I had reached an unhealthy level of weight, that I know now was negatively impacting my ability to do physical things. But I naively thought I couldn't possibly be getting heavier as I was still in a size 10. I was just either putting on muscle, when I was working out or had lost my muscle tone, when I wasn't. In my late 30s, I went up to a 12. I was unhappy about that, I'd lost a lot of weight when my DS was a baby but piled it back on and then some as he got older. But I still told myself I was just 12 and it was fine, all the while I trundled towards obesity. I know that the blame for that ultimately lies with me but vanity sizing really, really helped me lie to myself.
The reality is that you can no longer tell anything really about someone's weight depending in clothing size. The odds are that a short person in a modern 10, very probably is overweight and not just untoned. At a size 6 now, I know I'm both a little overweight and untoned, and am slowly working my way back to what's right for me while trying not to retrigger the post viral issues that kept me mostly in bed for over 3 months. Not because I want to fit back in my size 4 jeans. But because before I got sick I had become capable of things that were a complete dream to me, handstands, 360˚ jumps on skates, etc and I want that physicality back.