We are all learning here. It looks like a wire or thread. And it looks like it could be PMD. It is tough not having the coin in hand. Sorry I can't be more positive.
A strike through wouldn't move that much metal sideways. The bottom of the 5 got closed off and the lower 8 loop isn't round anymore.
I'll just say, my 1858 has what I believe to be a small strike through grease under the date. You can compare yours to mine. Based on the distortion of the 5 on your coin, OP, I believe it to be PMD, and not a mint error.
It has a low leaf reverse. There are actually four of these. I don't know what caused that under the 858.
If your asking about the abnormality at the bottom of the date, Looks like damage from the denticles of another (FE) coin.
Very interesting theory. I like it. The denticles on that FEC sure seem to line up as if another FEC caused that impression.
Where's the rest of that other FE on that obverse? There's why that theory doesn't make any sense to me. I think what we need to do is understand the date-punching process. Supposing this date-punch were punched over denticles by mistake. It was just punched too low on the die, leaving this deformation. The date-punch, itself, is now deformed. That same date-punch was then punched onto another die, as here, in the proper position. There we got it. This was simply a deformed date-punch that was subsequently put to use on another die. Think struck-through date-punch as opposed to struck-through coin. There used to be members here who knew how these dates were affixed. If anybody would have any such idea, today, I'd think it would be our big guy. As such, tagging @GDJMSP on this. Does this, a deformed date-punch, make sense? Then you can go, Doug.
I've never heard of or seen a deformed date punch. The die is softened by annealing, not the punch. There's a raised lip of metal visible along the upper edges of the damage, where the metal was moved. If it was on the die there would be many of these. Something hit the coin; what or how is probably unknowable.
That's the only thing. You're right, one would expect this to repeat if it were a deformed date punch. That would go against this being an isolated incident.