> Presumably, the actual criteria was likely familiarity and fluency for their tech founder or early developers.
That would be a completely valid answer to the question. The fact that they didn't answer the question at all is the problem here, not that they chose PHP.
In this metaphor the colour of the wall is equivalent to the product. The code is equivalent to whether the painters used brushes, pads or rollers or whether they used ladders or scaffolding - the customers do not care.
By asking why choose php you are asking why use rollers to paint.
If that's the case, asking about the choice of implementation language sounds like asking about the spec.
The end user does not care about the programming language.