That may have been a stud that screwed into the original alternator, and he just removed the stud and attached the wire to the alternator using a bolt or screw of the same dimensions and thread pitch of the stud. I don’t see why that wouldn’t work as well as the stud method. The only problem you might run into is that if that connection fails and overheats the screw, it might be more difficult to fix since the heating point will be closer to the alternator case; i.e. you can’t just replace the stud, b/c the stud isn’t there any more.
If you ever need to replace the alternator in the future, the connector problem – if there is one – can be solved inexpensively at that point. I wouldn’t lose any sleep over that.
If I were making the new connection from the wire to the ring-connector, I’d both crimp and solder it. That’s a more robust method than just crimping it. If you don’t see any solder, you might take it back and ask him to solder it for you. Shouldn’t be much of a fee for that.
The rubber over that connector is there mostly to prevent someone who’s working in the vehicle engine compartment from accidentally bridging that point to the chassis with a metal tool, like a screwdriver. That would create an inadvertent direct short circuit from the battery positive* to battery ground, and could burn or otherwise injure the person holding the screwdriver, let alone the problem of sparks mixing with any gasoline vapors in the vicinity. Even a slight possibility the alternator or other electrical circuitry in the car (like the engine computer) could get damaged itself if that happened.
There’s usually a rubber gadget over the battery positive post for the same reason. Suggest to improvise something if possible for both the safety of whoever’s working on the car, and for the car’s electrical system, even if it just wrapping some electrical tape (Scotch Super 33+ preferred). Most repair shops keep various rubber gadgets like that they’ve removed from other cars on-hand too to fix this kind of problem when it crops up, so asking your shop to improve that is another option. Asking an auto parts place for ideas is another option. Replacing the screw w/a new stud so it is like it was when new, yet another option.
- The big alternator post connects directly to the battery positive via that thick wire, sometimes without any fuses, but often there’d be at least a fusible link in that circuit which would offer a modicum of protection against an accidental short.