Antoine Van Laethem met Theo at a barbecue at their hostel Wake Up! and the pair bonded about their shared hometown of Brussels, he told an inquest on Tuesday via video link.

On the day of Theo's disappearance, Mr Laethem had gone for a long walk along the beach to the famous Cape Byron Lighthouse with another friend.

This is something he "might" have discussed with Theo, who was last seen being ejected from the Cheeky Monkey's bar at 11pm on May 31, 2019.

The police working theory is that Theo tried to climb cliffs at Cosy Corner beach, fell and was swept out to sea.

Why he walked in the opposite directions to the Google Maps route he had outlined back to his hostel, remains a mystery.

Antoine agreed the two from Brussels "clicked" and later wrote in a police statement that Theo "struck me as someone who is open-minded and can speak easily to people".

He recalled Theo was ready to leave Australia and was "pretty excited to go back home to meet his friends," and begin his engineering degree in September.

Video footage showed the pair later searching a local bottle shop for "cheap wine," settling on a two-litre box of De Bertoli Rose for $11, which they brought back to the hostel and shared with others.

He thinks they both consumed about three glasses because they didn't like the taste.

"He didn't seem that drunk or tipsy," Mr Laethem said.

The backpackers later caught a shuttle bus into town.

Mr Laethem said he remembered the night was particularly cold, and that the group never discussed taking drugs or showed any interest in doing so.

After the group gained entry into Cheeky Monkey's Theo's interactions with his new friend diminished and Mr Laethm said he had no idea he had been ejected.

So he sent him a Facebook message the following day with words translated to the effect: "Did you get home OK?"

Mr Laethem left Byron Bay on June 1 but later returned when Theo's cousin Lisa Hayez reached out, and he helped police with their search.

Counsel assisting the inquest Kirsten Edwards asked if he had thought about his own theory as to what happened.

"I don't know. I can't say, anything could have happened," Mr Laethem said.

The inquest continues.

Australian Associated Press