Actually it is related to how hydrogen was discovered.
Hydrogen was discovered by Henry Cavendish. He collected the air bubbles from metal-acid reaction and found this air to be inflammable. He named it "inflammable air", which later was given the name hydrogen by Antoine Lavoisier. Lavoisier name it hydrogen because he obtained water after burning hydrogen. The word "hydrogen" means "substance that produces water" (please refer to Lesson 16-5 for the suffix -gen).
|Cavendish's apparatus for making and collecting hydrogen. Source : Wikipedia|
|Henry Cavendish. Source: Wikipedia|
Although Cavendish was not the first person to discovered the air bubbles from metal-acid reaction, he was the first person who collected the air and characterized them. Therefore, he was recognized as the person who discovered hydrogen. He also discovered carbon dioxide by dissolving alkali in acids.