Why didn't you put "lets get the engineers ideas meeting before the yearly plan ships" as the meeting topic in the invite then? Otherwise you're expecting a whole load of people to turn up for a meeting with no idea what it's for.

If you don't tell people what the meeting is for, you're implicitly saying that they don't need to know the topic until they arrive, and so you're signaling that they're not expected to be giving input and they're just there to listen to something - and in 90% of such meetings, they could be done better by e-mail.

If you wanted feedback from the engineers, giving them a heads-up that this was their opportunity would have given them time to form their ideas into a succinct coherent point rather than an off-the-cuff ramble.