Yes, only ordained Anglican/Episcopalian priests can be ordained via the Pastoral Provision. Ministers from other denominations have sometimes been ordained but those are handled case by case, not via the Pastoral Provision. (Of course the Catholic church doesn’t actually recognize the sacramental validity of Anglican/Episcopalian ordinations.) Remember that Anglicans/Episcopalians are the protestant denomination that is most similar in practice and belief to Catholics.
And just because an Episcopalian priest converts to Catholicism, it doesn’t mean he gets an automatic Catholic ordination. He needs to be recommended to and by his bishop and then undergo several years of formation. His studies would be different from those of the typical seminarian because he already has some very practical experience with the ministry. As is often the case with married men studying for the deaconate, the wife (if any) usually undergoes much of the same study.
To the best of my knowledge, Anglican/Episcopalian priests are not converting to Catholicism in staggering numbers and of those that do convert, they are not all necessarily becoming Catholic priests. (I have no idea what percentage of such converts are married and do become priests.) Numbers alone make such priests exceptions to the rule that married men may not be ordained as Latin Catholic priests.