Comment by sagebird

I think it is best left unasked.

If you care to know, you can take a day to think about it. If it is not worth you thinking about it, then let it go. But if you care enough - Learn about what they did, scan the source code, look at how the tool is used.

If you come to the conclusion that they made a bad decision - ok - keep that to yourself. If you come to the conclusion that their solution actually is better, mention it to them enthusiastically and build a bit of trust with them by showing that you are willing to think and inspect, not just ask drive-by questions.

If you see someone constantly re-inventing the wheel, then look for an opportunity to discuss solutions before the next project begins. If you are showing up only during presentations, then you are too late to apply your knowledge. If the goal is to improve things and you are knowledgeable and clever, you need to be in the brainstorming business, not the "embarrass this guy during presentation" part.