Looks like porkbuns DNS runs on cloudflare: https://lowendspirit.com/discussion/4602/porkbun-ns-moving-t... https://kb.porkbun.com/article/216-how-to-enable-porkbuns-cl...
So it might have been a misconfiguration on porkbuns or cloudflares (or maybe a porkbun feature that requires the cloudflare cert) end that created a cert.
Seems like porkbun should be more clear about that using "their" DNS might lead to cloudflare issuing certs for those domains.
That would be the most likely scenario, yes.