Talnelat's blade most likely was bonded to him at this time.
The issue is that honorblades don't behave the exact same as regular shardblades. They can be summoned and dismissed like regular shardblades; but unlike regular shardblades, their standard behaviour seems to be somewhat opposite. What I mean by that is that a regular shardblade will dismiss itself immediately if it is dropped, unless the owner wills it to remain summoned. Honorblades do not have this feature.
You mentioned that human can’t bond Honorblades, but Nalan tells Szeth that his bond with his Honorblade has been broken. Can you clear this up?
Brandon Sanderson (paraphrased):
Humans CAN bond Honorblades. There's a crucial difference between Honorblades and Shardblades. When you drop an Honorblade, it does not disappear, even if it has been bonded.* A Shardblade will disappear when dropped.
source (emphasis mine)
Presumably, this stems from a few factors, such as the honorblades being more of a prototype for the shardblades that regular shardbearers and radiants use. Another factor being that (WoR spoilers):
Regular shardblades are mostly-dead spren. Honorblades aren't based around something capable of thought, so it makes sense to me that they don't react as automatically as a normal shardblade.
What isn't clear is if his bond was broken, or if he has just not summoned his honorblade yet. Taln is not in a good state of mind, so depending on how honorblade bonds work, it seems plausible to me that someone else was able to bond the blade after he dropped it. Either that or someone is carrying it around and Taln has not yet summoned his blade. I would assume the former, because whoever took it knew what they were doing, and likely wouldn't have tried if at any point Taln could just summon the blade away from them.
We don't know enough about how an honorblade bond works to speculate on how someone else could bond it though.