Paying someone else to do the work doesn't change who was responsible.
>Portugal was also the first country to officially forbid the slave trade.
In mainland Portugal, slavery wasn't abolished in Brazil until 1869.
>because in fact Lisbon had very few ones actually living there (it was not well seen in Catholic Europe to own slaves) and was mostly a point of passage (but then again, so were many Atlantic islands).
Catholic Europe didn't have a huge problem with it until the eighteenth century, they just had enough serfs that it generally wasn't necessary. Plus, this is about Protestant Portugal, and your source mentions that in 1550 10% of Lisbon's population was African slaves.