To me it sounds a lot like "We don't really want to answer that question, so here's a bit of technobabble to ease your mind."

I mean, writing your own linked list in C and then summing its values could be considered as having "a proprietary data model that calculates", but it has basically nothing to do with the question on how they track such things, just hints that they're not using an existing - and proven - tracking method.

To clarify; they took the question "How are you tracking installs" to mean "With your tracking data, how are you counting installs", and then basically answered "We add the numbers together"
This is a complete non-answer, and it seems to suggest that their actual tracking method is likely unreliable.