When someone is unwilling to participate in a chat or discussion it may be for a good reason. The above answer is a polite way of saying that he does not want to participate. 'Right now' means that he may want to talk in the future just not at that moment in time.
Henry appears to be taking a back seat in this discussion for some reason.
Henry seems to have nothing to contribute today
If you are 'passive' then you are an observer or non-participant in something. If you 'take a back seat' then it means you play only a secondary part in the proceedings. the first and third example sentences indicate Henry is saying little or nothing. The second sentence indicates he may be saying something but only on a superficial level.
"Passive"（受け身）な人というのは、単に観察する人または参加しない人のことを言います。
"Take a back seat"というのは、優先順位を後回しにし、目立たない立場に身を於くことを意味します。
例文①と例文③は、ヘンリーの発言が少ない、または無言であることを表します。例文②は、ヘンリーは発言しているかもしれないけれど、表面的なレベルでしか参加していない様子を表します。
He does not want to add anything else to our discussion.
We may be in a situation where we are having a discussion at work, school, or maybe a class we are teaching. Sometimes, there is a person in the room who does not want to add any points to the conversation and refuses to participate.
If we want to talk to this person, we can use some expressions such as:
1) He refuses to participate in the discussion.
2) He does not want to add anything else to our discussion.
私たちは職場、学校、または私たちが教えている授業で議論をしている状況にいるかもしれません。時には会話に何も加えたがらなくて参加を拒む人が部屋にいます。
この人に話したい場合、私たちは次のようないくつかの表現を使うことができます:
1) He refuses to participate in the discussion.
(彼はその議論に参加しようとしません)
2) He does not want to add anything else to our discussion.
(彼は私たちの話し合いに他に何も加えたくないようです)
He does not want to add anything to today's discussion.
*Name* is refusing to take part in today's meeting, so let's continue without him/her.
If someone is refusing to do something it means that they will not do it.
Example:
Q: Will you join the meeting today?
A: No! They are pointless and I refuse to waste my time!
To participate is to join in.
Example:
I will not participate in today's race as I hurt my leg.
もし誰かが何かをすることをrefuse(拒否)してるなら、それをしないことを意味します。
例：
Q: Will you join the meeting today?
今日、会議に参加しますか？
A: No! They are pointless and I refuse to waste my time!
いいえ、要領を得ないし、時間を無駄にするのはごめんです！
to participateは、～に加わる（参加する）という意味です。
例：
I will not participate in today's race as I hurt my leg.
足をけがしてるため、今日のレースには出ません。
When you want to explain that a person refuses to participate in a discussion, then you can say:
-He refuses to take part in the discussion.
-He doesn't want to participate in the discussion.
-He won't participate in the discussion.
ある人が議論に参加することを拒否していることを説明したいとき、以下のように言えます：
He refuses to take part in the discussion.
He doesn't want to participate in the discussion.
He won't participate in the discussion.
（彼は議論に参加してくれません。）
"Unwilling" is a way to say that someone does not want to do something. In this case, he doesn't want to participate in the discussion.
I hope that this helps :)
When you have a conversation or talk to someone this is also called a 'discussion' as you are discussing things with them
If someone will not do something then they 'refuse' to do it
To participate or join in mean the same thing and mean to be involved and included
人と話し合いすることを'discussion'と言います。
ある人が何かをしないことを 'refuse' （断る）と言います。
To participate や join inは、何かに参加するという意味です。
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