Contagion Engine and Mortarions Hammer?

Hey folks,
Kinds confused and bummed with our Faction Pack.

But besides the nerfs, i couldn’t find any keywords in the detachements. The contagion engine one states it cant be picked with another „engine“ dettachement, but i cant see this tag on mortarions hammer, even tho its basically the only other engine detachement.

Any ideas?