I am not sure about all of strong lifters have strong mind.
But as you say, this guy may have strong mind because of it.
Of course, physical strong or not, every person has his weak mental issues.
Sure, succeeding in things helps strengthen the mind, but without the right mentality you won't get far as a beginner. Look around you, in life and in the gym, and you can see how many people fail and how less people make the real difference.