The OP seems adamant that it's all real, and adds to his story in the comments. But does it seem like a being in character thing? (I sent him a PM saying ''nice creepypasta, are you going to write more?'') and he replied that it isn't a creepypasta and it's true. That it's haunted him for years and he is scared of the monster coming to kill him too. He seems pretty adamant that it is true, I am wondering what the reason could be for this. The sub he posted in has rules against non fiction stories.
I mean, it's not surprising the writer denied it being fake. I think part of the fun of these types of things is in not breaking kayfabe. It's like an in-joke - you definitely see it on r/nosleep, where they have the rule "everything is true here, even if it's not". Everyone plays along, because that's the point. I'd assume that r/thetruthishere either takes the play more seriously, or the people there do genuinely believe they've experienced supernatural happenings - most likely, it's a combination of the two. Whether this particular writer is one of the latter or is just dedicated enough tot he act to keep it up in private, who knows. But yeah. Why? It's fun, I guess.
Well travelling in time, monsters and exploding deer are obviously fake. He says it has haunted him for years.
The poster says s/he has "crippling anxiety". Anxiety can make people see/hear things that aren't real, etc. That doesn't mean it's fiction, it means the poster is presenting things from his/her perspective, and from that perspective this is real stuff.
Check out this thread for an exploding donkey... https://www.writingforums.org/threads/distinguished-service-cross-too-much.154742/
But can it make you see red glowing eyes? What about the fact that when he was close to it, all natural sounds vanished (such as the water flowing in the creek, and his own screams?) He heard the monster's footsteps, and managed to find a streetlight and clinged to it. The monster didn't come. He thought he would die. The waking up at 5 AM to wait for a ride for 3 hours, coming back in to find it's just turned 5 AM? The neighbor dying of black mould poisoning, when none was found in his home? He was 60 and never left his house. The deer he found that had burned from the inside?
If your problem is with the validity of the story, then assume it's fiction and move on. I honestly don't know what the issue is.