Was Metal Lee adopted?
Rock Lee is very similar to Might Guy even though he wasn’t his son. Both of them were similar in every manner, they couldn’t use Taijutsu, they had bushy brows and had similar habits.
Regardless, they were not father and son. Hence comes the possibility of Metal Lee being an adopted son of Rock Lee. If not adopted, what are the other possibilities?
Another possibility is that he married someone from another village just like Choji. As she’s busy with her work in the village, she isn’t being shown.
Also, there are rumours on forums ,which suggest that Metal’s mother could be Kurotsuchi, the fourth Tsuchikage of the village hidden in the stone. That could indeed come as a suprise, but again we didn’t see any bonding between them in the movie Naruto:Boruto the movie, the chances are low.
As of now, these are the only possibilites. As the show drags on, more possibilities will arise or they might actually show his mother just like how most characters are revealed. But the most interesting pair, I’d like to see is that of Rock Lee and Kurotsuchi.
These are mine and my only opinions. You might choose to agree or disagree with me, regardless I’d be more than happy to hear your theory on this topic.