After the defender was booed upon his homecoming to the club he spent 20 years at, Keane criticised the supporters who displayed such antagonism. Speaking on the Stick to Football podcast, Keane said: "The reputation of Liverpool fans is that they are loyal and a level up from most supporters.
"But I think for any player to go back, to boo him, people pay their money to go and that's fine, you're not going to argue with supporters."
He added: "Liverpool fans will obviously think 'We are the biggest club in the world' like all supporters. I'm not saying you give him the thumbs up for leaving you. But why would you go to a match and boo a lad who has played 260/270 games, stats are fantastic. You don't have to wish him luck in Madrid.
"But to go to the effort of thinking, 'I'm going to boo this kid' as a local lad and Liverpool fans for some reason think they've got class. No Liverpool fans have to have a good look at themselves.
"The beauty with Trent over the last year or two is that he has said very little, he's not been one to say, 'Oh I'd love to stay here.' He has actually kept his mouth shut and sometimes that's not a bad thing to do. How many times do you see players say, 'Oh I love this club' and then they leave. He kept it cool."
Following the encounter, Slot heaped praise on Alexander-Arnold's contributions during their partnership the previous campaign, during which the full-back netted four times and provided ten assists as Liverpool clinched the Premier League title in Slot's debut season.
The Dutch manager said: "He (Alexander-Arnold) lost so that is tough. I said something like 'keep going' to him. I honestly didn't know exactly what I said to him.
"He has been special to this club, he has been special to me. And he is a special human being. So, for me to give him a hug is something I will do every single time I see him."