If I used my Internet sniff test and was asked which of these two URLs is genuine, Of go for the putty.org one.

I'd maybe hesitate more if the legit address was clearly associated with a university (.edu or other hallmarks) but not even that.

When putty was written it was the era when people had personal websites and made software for fun or to help them in their daily lives.

It was a time people used mirrors, because while a connection to the far east was possible, it was painfully slow for a variety of reasons

https://www.chiark.greenend.org.uk/~sgtatham/putty/mirrors.h...

Since the late 00s though the world has changed and very few write software for fun, or to scratch an itch. It's always a hustle, waiting to be monetised or at the very least to pad a resume.

I like the fact part of the old world still exists in such a high profile area.