No nobody said "exactly that". But many times I've seen people claiming to trust open source as it is safer and people can check and build themselves. Seen it too many times. But reality is different than what is claimed.
You didn't use the word "safe", you used the relative term "safer", and on average, it is harder to hide ill intent in open source software, there's a greater chance it will eventually be discovered. The blast radius is larger for open source (because the barrier to using it is lower), which increases the number of people impacted, but an increase in the number of people impacted also increases the chance of discovery and motivation to address it once discovered.