There is an abuse ladder policy, so the punishment is based on the degree of the offense. However, each case is looked at individually, so a harsher offense could have been applied if it was seen to be warranted. You can find more info about the abuse policy here: Wayfarer Abuse Enforcement Ladder Policy — Wayfarer Help Center
Even if you did submit more than 1 nomination using 3rd party photos, staff may only note one instance in the emails as an example. So, even though you may have submitted more than one nomination with a 3rd party photo, they chose one as the example of why you are receiving the warning.
Like the warning notes, it’s best to review the Wayspot Criteria to make sure to are following them. The Photo Guidelines also state not to use 3rd party photos and other reasons for rejection, as well as what makes for a good Wayspot photo. And, if you have any questiosn about nomination, you can always ask in the Nomination Support thread, and we’ll be glad to help out.