He was testing your reaction to the text. I gather you don't make contact regularly.
The 'good to know' comment said to him, "I really don't want to talk with you, I'm just answering you out of politeness.'
If you had shown some interest, told him something about what's going on with you, or if you had asked him about his job, or his friends, or his cat...anything like that..he' would have responded to you.
But your response was disheartening to him. I'm sure he thinks you don't care about him.