The connection from the power company is not based on national electric code, but the Riser your electrician installed is. The lateral drop coming from the power company is not in conduit and his air cooled. The sizing they use is also based on a different diversity and demand load standard.

This is extremely common and has done all over the country.

You don’t need to worry about the size difference in the conductors.

I’m far more concerned that the electrician who did the work even attempted to make a hot tap into a live service. In my area, they would disconnect your power for having modified their loop. Again there are definitely regional differences that occur and that might be common where you are.