I would say there are substantial behavioural similarities (thinking styles and patterns, epistemic approaches, etc) that can be reliably observed, and despite their claims that they "have no opinion" on the existence of God, it's pretty easy to get them to slip up if one is debating from an actually neutral position. Also, they tend to have quite strong emotions on the subject for people who have no opinion.

Regardless, any such claim that it is another religion can be quickly debunked by a quick Google of a dictionary definition:

>> religion: the belief in and worship of a superhuman controlling power, especially a personal God or gods

The dictionary entry proves that atheism is nothing at all like religion.