>what is the standard deviation in that example...You need sample sizes to even attempt to do the math.

First, you're asking the wrong person to supply the missing data. The onus is on the OP to justify their stats, not on the person calling BS on the misuse of statistics.

Given that the original article is missing the critical numbers and presenting the rest in the most self-serving manner possible, the only data anyone has to go by is their own experience with conversion rates. We don't even know what "conversion" means for this website because they don't define it, but that justifies making reasonable assumptions (e.g. users who land on page A end up on page B, for a website in some industry, involving some side-effects to get from A to B that are left undefined by the OP). In my experience, the behavior of users on a web site is quite fickle and dependent on the surrounding advertising campaigns, as well as the weather, the time of day, and the timing of holidays. And maybe a billion other confounding factors. So, is the 5% improvement seen here significant? We don't know, there's no evidence to assume it is, and that's precisely my point.