The lines, spoken by Lennox, indicate that Lennox thinks Ross had a strange look in his eyes, lilke he had an odd story to tell. The irony is that, ultimately, Ross will have a very strange tale to relate. Ross can tell about how Macbeth killed Duncan, killed his friend, Banquo, and killed Macduff's family - all in the name of ambition. In this scene where Lennox delivers these lines, the Thane of Ross approaches Lennox and Malcolm. Ross tells them of how the Thane of Cawdor assisted the king of Norway in a battle against Scotsmen for some land. Ross says that Macbeth was able to defeat the Norwegian king and the Thane of Cawdor in battle. There is some irony, also, in that Macbeth was fighting for Duncan and proved himself very loyal against a traitor to the country. Later, it is Macbeth who performs a traitorous deed when he kills King Duncan. Additionally, Macbeth is the one in the end, who is killed in battle.
I am not very sure if your question relates to the following lines of Macbeth act 1 sc.2 :
" Norway himself
With terrible numbers,
Assisted by that most disloyal traitor,
The Thane of Cawdor, began a dismal conflict;
Till thatBellona's bridegroom......................"
In these lines, Ross reports to King Duncan how Macbeth accosted the invading Norwegian army camped in Fife backed up by the Thane of Cawdor. Macbeth proved himself a great warrior-- as if the groom of the goddess of war, Bellona--clad in armour proof against all offensives. The irony lies in the fact that Macbeth who proved himself so heroic, noble & loyal as opposed to Cawdor who was a traitor, was going to be the killer of the king and a vile usurper of the throne of Scotland. The fall of Macbeth was the fall of the most trusted and the most widely admired man, just as Satan who fell from Heaven was also the brightest of all angels in Heaven.