That's normal, the season ends in October but contracts run January to December so you often see riders in their 'current' team kit at training camps with their new team, i.e. Cavendish training in South Africa with MTN-Qhubeka/Dimension Data whilst wearing Ettix-Quick Step kit.
Kittel's case is unusual as he's not wearing Giant-Alpecin kit, nor is he riding a Giant.
That's normal, the season ends in October but contracts run January to December so you often see riders in their 'current' team kit at training camps with their new team, i.e. Cavendish training in South Africa with MTN-Qhubeka/Dimension Data whilst wearing Ettix-Quick Step kit.
Kittel's case is unusual as he's not wearing Giant-Alpecin kit, nor is he riding a Giant.