Sage 54.
[…]
For the first time since Sebastian started asking the system questions, it kept quiet for more than 10 seconds without answering. This reaction alone confirmed his suspicions.
During the previous battle after Octumpedam emerged from the hole, when the situation became too certain of death, he was scared and had no choice but to pathetically call his system for help.
The reaction of the system then was what made him suspicious. He didn't think about it immediately then due to the tense situation but after the battle, he finally started noticing the strange trends.
Though he was not an avid fan of novels in his previous life, he still read novels enough to know about systems.
He may be wrong but from what he knew about systems, it was abnormal for a system to provide help to him in such an inconceivable manner. Then, it was like a motivational speech from Eric Thomas himself to him.