You did nothing wrong. The seller's agent was hiding something from you. You may report this non-ethical conduct to your state RE commission for possible disciplinary action. You deserve an explanation. The seller agent didn't follow an open bidding process and refused to give everybody a fair chance counter offer process in multiple offer situation.
Check with your buyer agent and see if he can consent in this matter. At least you may ask your agent to report this to seller agent's brokerage.
