Were there spies involved? Im sure that they both had knowledge of previous research done by the Union before the south seceded. But the timing was so perfect.
Because Ironclad ships themselves were nothing new.
The Royal Navy(Warrior was the first) and France(Glorie was the first) had begun an arms race with much larger and more effective oceangoing Ironclads several years earlier.
But yes the Union received reports of the raising of the Merrimack's hulk, and the intent to convert her. Spurring Lincoln to support the Union's crash build program, of which Erickson's Monitor design was only one, and arguably not even the most effective.