It may well be that your singing is getting better. When there are a lot of things wrong with someone's singing, it's hard to give constructive criticism --- where does one begin? But when the singing is pretty good, and there are only one or two things that could maybe use improving, then perhaps it's worthwhile to talk to the singer about those things.

But I think it's more likely just coincidence. We look for patterns where there aren't any; many things just happen, with no rational explanation. See if it continues, or if it goes away as quickly as it came.