Why? cuz my password was leaked?
If they know your email address and know/guess you have a Garmin account, anybody can ask for a password reset.
It's vaguely possible that that person's email address is close to yours and they have a Garmin account and mistyped the address.
If the temp password works on the actual Garmin website, then change the password to something safe (and don't worry about it).
If you use your real email for your apps and "contact developer" A user will have your email and can request a password reset for your account
The email I use for "contact developer" isn't my normal email address so users don't see my real one
The email I filled in Contact Developer is different from my garmin account. But I don't know why. Maybe cuz I used my account in some gihtub actions