Just an SLF here (in Portugal so TAP are my home team!) but my first thought was also that cameras do lie so there would be some rational explanation such as the ground sloping away out of sight so perfectly safe height AGL when he commenced the turn.
What are the rules about how high it's safe to start a turn? It should be no different for a regular flight with pax aboard or an airshow for fear of collateral damage on the ground.
Until I hear - from a readout of the FDR etc., not YouTube! - this crew broke rules, I give them the benefit of the doubt. Indeed (to be more positive) I've seen nothing to make me doubt the professionalism of TAP Portugal.
Rgds, M63
PS I voted in the poll "I don't have a view" because I'm not qualified to express a view, one way or t'other.