sadly - I find that blog article empty.
nicely written, good theory overview, near zero practical value

> enough trades (say 50+)

that's like couple days

to my mind - tells nothing

> not a guarantee for robustness

I don't believe there is any

> This largely depends on the complexity of your approach, the more complex, the higher the likelihood of over-fitting.

already mentioned - think it's much more important when working with machine learning

> Believe me, even with 10 years of data with 1000+ trades you can have over-fitting

I know it's there. just don't think it's that easy to pick it out by delaying tests on some particular data