I get a ton of emails in my line of work, many of which are just letting me know that so-and-so can't make it today. Giving even a brief reply to every one of them gets exhausting. So at this point, I reply only if I really need to. "Thanks for the info" and such are not really necessary, IMO, unless an answer is specifically requested.

So, OP, I don't think your T is upset or testing you. I think he just didn't see the reply as urgently needed and chose to do something else first.