'Thundering' may imply 'bold' or 'loud', not 'angry'.
From The Buddha's Last Days,
The the venerable Sariputta came to see the Lord, saluted him, sat down on one side, and said, "It is clear to me Lord that there never has been, will be, or is now another ascetic or Brahmin who is better or more enlightened than the Lord.
You have spoken boldly with a bull's voice, Sariputta, you have roared the lion's roar of certainty! How is this? Have all the Arahant Buddhas of the past appeared to yu, and were their minds [etc.]
Loudness and/or confidence must have been useful, in a crowd: from The Lion's Roar,
It is not typical of the Buddha to extol himself, for he did not intend his Dispensation to evolve into a personality cult centered around himself as a charismatic and powerful leader.
[...] "Here, the Tathagata understands as it actually is the possible as possible and the impossible as impossible. And that is a Tathagata's power that the Tathagata has, by virtue of which he claims the herd-leader's place, roars his lion's roar in the assemblies, and sets rolling the Wheel of Brahma.
Maybe too it was part of a style of oratory: from Kim,
Hereat, simply as a child engrossed in a new game, the lama threw back his head and began the full-throated invocation of the Doctor of Divinity ere he opens the full doctrine.
The "Lion's Roar" seems to be repeated in this Zen story: from The Last Poem of Hoshin,
Hoshin, with the roar of a conquering lion, shouted "Kaa!" and was gone.
As for displaying affect, No Attachment to Dust suggests,
Even though alone in a dark room, be as if you were facing a noble guest. Express your feelings, but become no more expressive than your true nature.
The Buddha explicitly warns against reacting to an insult with anger: from Akkosa Sutta: Insult
Whence is there anger
for one free from anger,
tamed,
living in tune —
one released through right knowing,
calmed
& Such.
You make things worse
when you flare up
at someone who's angry.
Whoever doesn't flare up
at someone who's angry
wins a battle
hard to win.
You live for the good of both
— your own, the other's —
when, knowing the other's provoked,
you mindfully grow calm.
When you work the cure of both
— your own, the other's —
those who think you a fool
know nothing of Dhamma.
