This is speculation but if the boy had higher levels of T his body could have already been producing a higher then average amount of estrogen.
I actually had blood drawn a couple of weeks ago to check for this very thing. I’m male, and while my testosterone levels are in the median range, my estrogen levels are very high relatively speaking. I’m operating under the assumption that it’s caused by recent weight gain - thanks, quarantine - so I’m working to lose that weight and will check it again.
Interestingly, there don’t seem to be many accepted options for reducing estrogen levels. My PCP suggested broccoli seed extract, but made it clear that it wasn’t a well-supported or accepted treatment. The most reliable treatment is a change of lifestyle.