Did the OP just take the opening companies quote and say I can copy this to a tee, same price and all after the furniture was sold? Is this ethical, more ethical than the original company trying to save his bid by discounting?

If the OP can't and/or didn't just offer his preferred furniture line the job must have been sold, value built in that specific brand. The customer mentions to the OP that he's getting the furniture and shows quote. OP says no problem, I can match the quote. Other company follows up with who knows who on a bid they may have thought was sold, and was.

Taking other peoples work backfires on OP and other company as they are forced to discount. ID and/or furniture manufacturer remain loyal to their connections.

This could have been avoided by the OP doing leg work and trying to sell the furniture upfront himself. Something like gee Mr Customer, this theater is going to be fantastic, what do you plan to sit in? Then he could have built a quote himself.