Hi Grae,
Thanks for reaching out to the PayPal community forums. That is very weird! It is possible that this individual had Canadian dollars in their account and sent them to you or that their account or your account is actually a Canadian account. WIthout speaking to PayPal customer service, the specific reason may not be available.
You can check your payment receiving preferences to block payments that are not in your preferred currency. Here is a link to a helpful article to assist you with that: https://www.paypal.com/us/smarthelp/article/payment-receiving-preferences-faq2406?app=searchAutoComplete.
By the way, you can refund the payment so that the sender can try again after editing your payment receiving preferences.
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