I feel like I should point out that pure lead is really soft. So soft in fact that you should be able to easily scratch and deform it with a dull knife. Lead will also tarnish really quickly when heated and turn a flat grey color. Because of its low melting point, lead would also be a really bad filler metal for cast iron cookware. It would soften and fall out if you ever overheated the pan.

Try scratching a line through both the pan and the brighter area with the tip of a fork or a dull knife. If it’s lead, the shiny area will scratch much deeper and feel different compared to the cast iron.

Also, filling a hole or a void with lead might be easy, but welding with steel is also easy and probably cheaper from a manufacturing perspective.

I am far from being an expert, but I would think the shiny spot is indeed a repair but with arc welded steel or an iron/nickel alloy. Both of which will be durable, stand up to heat beautifully, and also appear noticably shinier than cast iron even after being heated on the stove.