I believe endorsements on LI are fake. I'm receiving endorsements for random things from my former and current co-workers and I know for sure they never sent any (either because I asked them or I know it's entirely outside their expertise).
And I allegedly endorsed someone for "TeamCity" before I knew what it was!
Either they're faking the data or their UI design is negligent-to-malicious levels of bad.
I am not sure about anything on LI page - it so full of dark patterns that spamming random people with invites is always at most 2 clicks away. It might be similar with endorsements.