I like to think when Crane looked down his neck he realized it was Brom, which wouldn’t exactly make the situation any less horrifying.
I look at it this way: for most of the story, Crane takes no one seriously, Brom included. He walks all over everyone and manipulates his way constantly into getting what he wants. He’s used to that. As a result, he probably thinks of Brom as just another dummy he can trick.
So IMAGINE the UTTER HORROR of realizing, for the first time in his life, his little tricks have caused some blatant murderous rage from someone. Someone he very much underestimated. I mean, Brom DOES try to chop his head off on multiple occasions throughout the chase scene. He could’ve just chased him a bit and let him cross the bridge and let Crane’s superstitions do the rest of the work (since that’s when the HH’s power would be gone). But no, he chased him the entire way, constantly slashing at him with a very real machete and throwing flammable shit at him. Hell, Crane nearly DROWNS because of Brom. The message is simple: get out of town or I’ll get rid of you myself.
It’s also a much more satisfying moment when you consider the beginning. Nobody messes with Brom when it comes to Katrina, in fact everyone immediately stops trying to court her the second he shows up. And yet, Brom’s described as, from the town’s perspective, as a non-malicious prankster. What are they so afraid of if he’s not publicly mean? Crane’s probably wondering the same thing, considering his lack of hesitation in courting Katrina despite Brom’s obvious love for her. I think they know that the one thing he’ll lose all restraint over is Katrina. Crane doesn’t realize this until it is far, far too late.
That’s where I like to think the real horror of Disney’s Sleepy Hollow lies. It’s about an otherwise beloved man who flips on a switch and kills someone for the woman he loves. And because of his hero status, the town enables it and maybe even covers it up.
Oh and uh Katrina MARRIES BROM shortly after he does this. Which uh. I dunno if she knows, but if she does that’s just cold.