You have it right, an Infiltrator unit, if deployed in a transport cannot infiltrate, however, they can outflank. Because the tank has to move onto the board, troops that disembark on an outflank cannot assault.
BGB p.94 wrote:Note that if such units are picked from their army list together with a dedicated transport, they may outflank [...] embarked in it.
BGB p.94 wrote:When a reserve unit arrives, it must move onto the table
BGB p. 67 wrote:If the vehicle has already moved [...] After disembarking, these models may shoot (counting as moving), but may not assault.
EDIT: adding rules support.