First, Catholics are indeed in communion with the Pope–and with Christ and with their fellow Catholics, and with their fellow Christians to an extent and even to nonChristians in so far as all people are the children of God.
Second, you don’t think that Benedict (or for that matter any given person) is in communion with Christ and with himself as well? That doesn’t make much sense.
Third, one of the prerequisites of the Papacy is that the holder be a 'Baptized male". . .and even if Benedict had a valid “protestant” baptism that would be a matter of public record. For the record, the only recorded baptism of Benedict was Catholic.
Fourth, a person baptized Catholic is (according to many canon lawyers) always Catholic (and we have heard of no formal abjuring of the faith by Benedict).
I could go on but the preponderance of the evidence seems to be pretty heavily on the side of Pope Benedict being Catholic, doesn’t it?