Oh dear, what a day!
But it turned out all right. We all know that head wounds bleed particularly heavily, so of course you quickly panic. But you did everything right, don't blame yourself! It's futile in the long run, because you definitely can't prevent such accidents. Not even as a "helicopter father" (which, as we know, is pure poison for the child's further development towards independence).
Of course, the five-year-old has to learn to assess his strength. This is not very easy at that age, as they are only just beginning to perceive their own body pattern. Talking and explaining (even forbidding) doesn't help that much. Let him experience it in the action: Play with him, romp with him. Play "pushing" with him and gently show him what much more power (in this case yours...) can do.

As a football fan, you might like this anecdote where I suffered a similar injury as a small child: 1974. I was four years old and sitting on my father's lap watching the World Cup final on TV. With the final whistle, Germany became world champions. My father jumped up in delight and the child fell with his head on the edge of the table...
I will never forget the names Paul Breitner, Gerd Müller, Ulli Hoeneß and Sepp Maier... ;-)