Rereading some of the material about the Ardennes offensive and Operation Barbarous, I noted that in Panzer Leader, Guderian barely mentions Manstein, even though presumably they were relatively close colleagues. If all you knew about those operations was from Panzer Leader, you'd hardly know that Manstein did anything at all. Was there some personal reason for this? Is Guderian just being a glory hound?
I'm assuming by "Ardennes offensive" you mean the 1940 fall gelb and this answer comes with the caveat that I haven't actually read Panzer Leader as I found it impenetrably dull.
However, while Manstein originated fall gelb and managed to get Hitler to accept it as the de facto plan for the invasion of France, he made some enemies along the way. These included Halder and Brauchistch who felt threatened or embarrassed by the fairly obvious intellect of their insubordinate subordinate.
As a result, Manstein got kicked out of his staff job OKH and placed in charge of an XXXVIII infantry Corps which had no part in fall gelb. Thus although Manstein handled his Corps in exemplary fashion in fall rot, this was hardly going to feature much in the autobiography of Guderian - himself in command of a Panzer Corps in fall gelb.
In Barbarossa again, Manstein was merely a Corps commander and again, no matter how well he handled his Corps, this was an operation on a massive scale and the actions of Corps commanders are unlikely to attract much comment in an operation dealing with multiple army groups.
So really when you say
you'd hardly know that Manstein did anything at al
He was kind of junior in terms of overall operational command. However, when you say
Is Guderian just being a glory hound?
its also unlikely that Guderian is going to dedicate too much space to giving credit to another officer, an understandable and expected example of bias in an autobiography that does not require personal animosity to be explained.