
This is a vision he had of a possible future, which is why he begged baby daddy to get him pregnant in the first place, so he could avoid that future vision coming true.
Now we see that there is a chance that the vision was not originally the old man, but instead the evil old guy who is now using his face as a disguise.
I believe that we are seeing more of the future vision that wasn't revealed before, showing the young buzz cut grandpa assaulting MC.
With the way the evil guy is able to transform after eating people, it possible that the buzz cut in the vision is also him, but that's all speculation at this point.

There was a flashback or two in previous chapters (sorry I can't remember which) that showed him basically in the same cage/cell and the old man was on the outside of it. If I remember correctly, the MC had shorter hair in the vision so maybe it was meant to imply he was younger in that scene than he is now (which is why he may have assumed he managed to avoid it).
My memory is a little iffy, so I could be mixing up things that happened in different chapters but I think so far we've only seen that vision in parts, about 3 times total including this newest bit.
Is this a vision he had in the past about the future and hasn't happened yet. Or is it a vision of what happened to him in the past. I thought the first but unsure