Aside from being extraordinarily late (PHP has been available on App Engine for quite some time, so its quite late for any story about that support with the claim that Google is only just acknowledging the existence of PHP), the article seems premised on the idea that the reason PHP was not on App Engine earlier than it was is that Google was somehow in denial about it existing.

I think its a lot more likely that App Engine was initially Google making internal infrastructure available external users and that the launch languages were set by what Google was using, not what Google was acknowledging existing in the external marketplace. The inclusion of PHP was one of many signs of the App Engine maturing as a product, but its prior exclusion wasn't Google denying that it exists.