My guess is he’s not anti-immigrant, but probably thinks the Church should be focused on religious worship and on helping the poor (they have a soup kitchen which is still going, although he’s getting a non-profit in to run it) and not on hanging banners and making political statements.
Many of the African priests are pretty conservative and into restoring reverence to the Mass and so forth, like Cardinal Sarah.
He could also have a very valid concern about the banner suggesting to the authorities that there are illegal immigrants frequenting the parish church. I’m pretty sure any actual immigrants in that community would rather not have attention being drawn to their presence.