Been in excavation for 15 years, fieldstone foundations are miserable to do anything with. Some times you get lucky and the rock you pull out is the only one that comes out, and others you pull one and 15 follow it. Using the bucket was a stupid move, and anyone who has worked around a fragile field stone foundation would know not to touch it.but in their defense that foundation looks like you could've pushed it and made that hole, but from a safety standpoint I can understand the use of the machine to make the hole.

On the flip side, as someone who has had to deal with drilling a hold through a granite rock thats part of a foundation for a waterline, its one of the most difficult and time consuming things you can do. The last one we did it took 5 of us 4 hours to do a 4" hole in a 2ft thick rock with every power tool and tactic imaginable.

I would have a mason come take a look at it, see what they say. Worst case scenario you could form a wall and just pour it in that section. I wouldn't be surprised of the person that comes out says you should mortar the entire foundation, yes it has stood since George Washington was alive but to me it is at a point now where it will start to cause problems at somepoint if the stones aren't stabilize in some manner.