Does my friend's and my laughing at an incident mentioned by an elderly man in the mosque, without his noticing us, count as backbiting?

It is forbidden to imitate an elderly man with the intention of mockery or disdain, as this is harm, backbiting, and slander. This action is encompassed by Allah Almighty's saying: "O you who have believed, let not a people ridicule [another] people; perhaps they may be better than them; nor let women ridicule [other] women; perhaps they may be better than them. And do not insult one another and do not call each other by [offensive] nicknames. Wretched is the name of disobedience after [one's] faith. And whoever does not repent - then it is those who are the wrongdoers." And: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful." And: "And those who harm believing men and believing women for [something] other than what they have earned have certainly borne slander and manifest sin." And: "Woe to every slanderer and backbiter." Mockery involves belittling and disdain, and it can be through words, actions, gestures, or indications. Backbiting is not limited to the tongue but includes any action from which a deficiency in the person being backbited is understood, such as imitating his gait, and it can be more severe than backbiting with the tongue.