I don't believe this describes a separate species or cultivar, but perhaps it describes the place of origin.
Are they bulbs or rhizomes? If they are bulb irises, they may be Dutch. Holland and Belgium are right near each other, maybe that's the source of the confusion.

Or he could have meant bearded rather than Belgian. Do you have a photo of these irises in bloom?

Renee

It's definitely not a bearded iris and it's not a bulb. I think I'll just have to wait until it blooms. I was hoping someone was familiar with Belgian iris.

I'd be interested in seeing it, because I couldn't find any reference on the Web except the Belgian Iris Society. Good luck with your ID!
Renee