The ten assassins were all confused, as well as scared for an instant.
Lyle's smile was an obvious sign that he had noticed them and that he knew exactly where they were. They had been found out by him, and they had no idea how it happened.
None of the two assassins who were sent to stalk and poison Lyle had sent them a signal, and since the signal only took a mere instant to be sent, a gentle touch to the device, a light channeling of mana to it, even if the enemy was a Golden Knight and the two assassins were Silver Knights, they should have had enough time to notify them.
Lyle was injured after the battle against the Necromancer. He had almost lost his life, they were certain about it as their information was impeccable.
They knew that he was now much weaker than normal, which was why they didn't use Golden Knights to stalk and poison him, but Silver Knights.