Hisoka is impressed by Gon's potential and Leorio's courage. After knocking Leorio unconscious, he tells Gon they both "pass" his test. He carries Leorio to the next exam site himself after receiving a radio call.
In the manga, the does not actually swallow Gon and Killua. Hunter X Hunter 2011 Episode 5
The anime omits a character named , who runs away with Kurapika and Leorio in the manga version. Hisoka is impressed by Gon's potential and Leorio's courage
First time watching HXH (2011) here! Episode 5 : r/HunterXHunter Hunter X Hunter 2011 Episode 5