As a lawyer, though, he has a responsibility for the contents of his filings. And there are legal standards for how to research and verify these things — which he didn't follow.

I am curious if an architect or an engineer did this for a design and submitted this, would we extend to them the same "reasonable" explanation and excuse, especially if someone's life was put on the line.

Interestingly, it's exactly the same in court! People's lives are put on the line all the time, and lawyers also sometimes flat out lie. This just further indicts the current legal system because it doesn't really "work" but it's just that the mistakes are often covered-up enough until most people forget about them and move on to something else.

And he didn't bother to verify the facts before he presented them in court? That's scientifically/logically/professionally unsound and irresponsible.

But it’s not deliberately lying

If you sign you name under "I declare under penalty of perjury that the foregoing is true and correct." then you absolutely have an obligation to check that your facts are correct.

Then no one would ever sign. That's why it says "to the best of my knowledge" as part of the statement.

"Your honour, I am not a cat"