Van Dijk led his side to a 3-0 success in Saturday's fourth-round tie.
They led through a Curtis Jones strike late in the first half but then survived big chances from which Jack Hinshelwood and Diego Gomez should have scored.
The Reds skipper stopped to speak to reporters as he left Anfield and the opening question was along the lines of his side having had quite an easy ride into the fifth round.
He responded to that “it was comfortable” suggestion with two questions of his own.
Van Dijk said: “Comfortable - you think so? Did you watch the first half?
“I think Brighton, and especially in the last few years, can make it very uncomfortable for teams.
“We were trying to press and they were playing through our press.
“You go in at 1-0 at half-time and you know the game has still so long to go and changes can come.
“The scoreline maybe makes it look like it was a bit comfortable but I think it was still very hard work.”
Liverpool boss Arne Slot said Albion’s style suited his team.
He added: "It was two teams wanting to bring the ball out from the back, which you don't see that much anymore in the Premier League.
"Margins were maybe smaller than the 3-0 looks like because at 1-0, just before half-time, they got a big chance.
"In the end it feels like a comfortable win but I think it was closer than the 3-0 score shows.
"It was possible to press. Many times this season when we played here it wasn't possible to press becasue of the style of play of the other team.
"I said before the game, today we have two teams with a similar style, who want to bring the ball out from the back and two teams who want to press high.
"The modern Premier League is a lot about a direct style of play and a lot about set-pieces but today we faced a team who want to bring the ball out from the back."