can't help but do 和couldn't help but do 只是时态的区别吗?

can't help but do 和couldn't help but do 只是时态的区别吗?
站在这美丽的森林中,他情不自禁地深呼吸.为啥翻译成Standing in the beautiful forest,he couldn't help but have a deep breath.为啥用couldn't 不是 can't,因为这个句子是过去时吗?