Well, no, not really.

Being a "grower" isn't the same thing at all.

Someone putting on weight could be called buried penis. Totally different thing as well.

Libido loss doesn't have anything to do with the penis itself, directly. There may be an underlying hormonal issue that causes both, but that's still different. And, sometimes people with micropenis may have psychological issues with their penis that interferes with libido as well. But, again that's not the same thing.

And, no, it doesn't "turn" micro later. By definition, it's an inborn thing. It would be called something else if it happens later in life.

The most recent research into this is barely a year old, but it only backed up and refined previous information; this stuff has been documented and studied since at least the seventies, since that's when the first surgeries for altering the condition took place. And that's just as far as I know currently.

It's maybe one of those things where there's a gap between the actual definition of a medical term and the colloquial usage, but I'm going off of the medical version. Again, from that standard, it is inborn, with the key factor in causing it being hormonal abnormalities in utero. The reasons for those hormonal issues are varied, and may have other symptoms after birth, but for it to be micropenis instead of something else, it's an in utero malformation.