He says he thinks it was hit with the mower.
If he just patched it, don't you think the mower will hit it again? I have suggested cutting the whole mess out and burying it deeper or back filling around it so it is not exposed to another mower strike.
Besides this is a two dollar part, you will spend way more than that on your patch. Once he gets it in his hand and posts a picture, it will be easy to identify. They don't make that many kinds of plastic elbow.