I've noticed that gy can sometimes sound like a really soft english J, like in Justice. Some words seem to slur slightly, so it could be possible that the unvoiced sz is unvoicing the gy, making it seem like a T. I think Icelandic does something similar at the end of words though I could be wrong.
A: Ez egy szék? B: Igen, ez egy szék. A: És ez egy szék? (*) B: Nem, az egy asztal.
(*) The english "but" translates to "de" or "azonban" in hungarian. The literal translation of "És ez egy szék?" is "And is this a chair?", it is a bit different from the english sentence you provided, but I think this is closer to the intended meaning.
Another possibility could be "Azonban ez nem egy szék, ugye?" which would translate to "But this is not a chair, is it?".
wait a minute. In the previous exercise it was like a "Ez asztal, nem szék. - This is a table, not a chair." so why is there no "egy" but still А chair and A table? that's ok with English cuz it must be either A or The, but is this not necessarily in Hungarian or is there some rule that I should know?
There are no strict rules about it but I would say, without any articles, it sounds a bit more like an adjective, a property describing the subject. "This is chair enough" "It has a high enough level of tableness" :D "egy" means "one" too, after all, so using this article quantifies it as one single instance. Sometimes, it feels more natural to imply the amount as "exactly one", sometimes it feels more natural to append it as an unquantified property.