Weird chainring

I had the chainring set replaced on my MTB commuter a couple of weeks
ago but just noticed Wednesday night during the post rain cleanup that
the middle chainring has a strange set of teeth. They seem to correspond
with where the cranks are but the remaining teeth are standard. There's
a couple of smaller teeth and a larger tooth that is slightly hooked.
Just wondering if anyone can explain what this is about and why it would
only be on the middle chainring??

DaveB