At the moment, the mentorship module picks any username listed on the mentors list.
If a link to a userpage is made somewhere else in the page, this name is picked.
This has been noticed on cs.wp so as on fr.wp (can't find the link back).
Since we plan to scale, it won't be possible to check every mentor list. A way to avoid mistakes would be welcomed.
I think the best solution would be to manage this using a special page, but I get that's going to be more difficult to write.
We're heading towards deployment of Structured mentor list to Growth wikis. Once that project's deployed, we won't depend on userpage links in the mentorship list. With the deployment of Structured mentor list, making the wikitext-based mentor list more reliable will not be necessary anymore.