He won't reveal his second power because Dark Knight might be eavesdropping, but he's willing to reveal his whole plan otherwise. There could, of course, be explanations for that, but a few of the people present might wonder about it.
Exactly what crossed my mind as well. Even if we in the audience know his true reasons for being tight-lipped about it, the others in the meeting would surely get suspicious about these double-standards on his part.
A few scenarios I can think of at this point:
1) He's bluffing about his strategy to face Darknight- in which case he's throwing off not only Darknight but also the women in the meeting as well. How he plans to accommodate for this double-edged sword would then remain to be seen. (IMO the most problematic scenario - see above)
2) The whole "bluff" is a misdirection/red herring to begin with, and his winning strategy doesn't depend on anything discussed in the meeting, but instead relies on something Dahlia can do from a safe distance from the front-lines. (Potentially less problematic if their suspicious reactions don't affect the outcome either way)
3) The very claim that Darknight could be listening in is itself a convenient lie to keep his secret to himself - having found a way to prevent any such eavesdropping through yet another ingenious deployment of slimes or other similar countermeasures. (This would also be compatible with point 2)
I'd love to hear from others if there are additional problems with any of the scenarios I've come up with above