It is exactly correct to say that it's the defensive player who is most at risk there. And you're right that the coaching point is always to keep your head up and "see what you hit".
That's easier said than done in practice though, and the angles they were showing on the broadcast last night made it look to me like he dove in for a shoulder tackle and Fields changed lanes into his head.
But based on the slow mo angle which appears to show a purposeful spear (which by the way was illegal 25 years ago, that's not new) it was clear he was going to be gone.
Still, as in my original comment, same hit but an RB pops up after it and trots back to the huddle no one would have batted an eyelash.