Hole in PCB due to corrosive reaction?

It's unlikely.

• The hole is very nearly circular, and has smooth edges, indicating the hole was deliberately drilled.

• Somebody has added thin wires to try to repair the damage, indicating the defect was found and "repaired" before the product left the factory.

Most likely the hole is meant for mounting the board into the housing. The damage to the surface layers is a fabrication defect that they tried to fix rather than scrapping the board.

Edit: As pointed out in comments, another possibility is that the hole was drilled deliberately to remove some incorrectly designed wires, and then the added wires you see were added to replace the connections broken by the drill.

Those wires you see aren't the bonded copper traces, which you think are left behind from the corrosion. They are wires added after the fact to correct the broken board. You can tell by the blobs of solder that were manually added, like the blob above the carbon trace that is not perfect (unlike what you see from wave soldering), or the solder added to the trace above that (north west of your red X), which you would never see on a etched board.

Considering that holes are normally drilled after most of the board is done in a typical PCB fabrication, and if it was a one off problem that would have been pitched, this is likely one of MANY boards that look exactly like this. The cost benefit of ditching these and a second run probably exceeded the cost of having these reworked manually. Material is more expensive than labor over there. The source issue was likely fixed before the next batch, but retooling a manufacturing process is also expensive, so who knows.

As to how that happened, speculation but:

• Drill was too big for the material OR
• the wrong bit was mounted OR
• the speed/torque was set wrong, so it chewed up the PCB material OR
• the depth was off so the collet holding the drill bit crushed the board OR
• Questionable material. Material is cheap, Labor is cheaper, but that leads to quality issues.

Corrosion does not make perfectly round holes in PCBs... The edges of the hole kinda look like a crater, soldermask and tracks have been ripped off like someone hacked at it with an x-acto knife.

There are several copper wires soldered across the hole...

This looks like a very "ghetto" botched repair job.

Now, what does the virgin PCB looks like? A bit of internet search and...

There doesn't seem to be anything in the area of the hole that would blow up and then require someone to fix the damage, like a tantalum capacitor. Also, an important detail is that there is no hole on the original board.

So, where does the hole come from?

Now, the edges of the hole are really destroyed. This wasn't done by drilling. It looks like it has exploded.

I'm going to go with the hypothesis that this controller was shot with a .22LR bullet from the back of the board (referring to your photo), then refurbished. Please check if the diameter of the hole is the same as a .22 bullet, I'd really like to know!