He had been careless. Jack knew that. He should have seen the trap coming. Evolvers below Level 5 were barely wielders of energy. Only crude application of it could be displayed by them before integrating it onto their existence and ascending.
So he should have noticed the connection from the beautiful alien to the water she had dispersed around. He should have taken it into account that she was preparing something, and readying a layout to pull a fast one on him.
Moreover, his lack of experience got him. While his new form of energy had been recognized and named before he could even explore its deeper mysteries, he had been thinking that her water only had greater viscosity up to now due to how it didn't flow as it should have when it hit him for the first time.
Mistakes on top of mistakes, plus a dash of overconfidence and some overflowing instinct of reproduction to make him distracted just for the necessary split second.