It's actually not that clever. To start with, the offending document details not just one peson, but several people's work arrangements, so from a purely personal safety angle it means that anyone looking at the roster details would know when these staff would be out of the country.
Secondly, the information in question is personal to the individuals concerned, consequently it would probably fall within the remit of the data protection act.
Now you could argue that leaving this around on a photocopier was slack, but there is a degree of trust that one has to have with colleagues. Whoever decided to put this information on a public forum clearly is not worthy of such trust.
Put it another way. If a member of the cabin crew scheduling team were to publish the rosters of the BASSA reps, the union would be baying for blood and expect the instant dismissal of the offender. So how is this action any different ?