There are many different ways to cut up how Google operate to present the idea that it is more of an ad company or more of a tech company - the fact that both of these are possible leans further into calling it an advertising and tech company. For example by looking at profit Google's ability to operate and exist comes from ads, on the other hand most staff at Google are from STEM fields and Google's aspirations are clearly tech driven, even if it uses ads as the means to an end.
I feel the expression "Everything should be as simple as possible, but not simpler" applies here. Labelling Google as tech-only is as provably false, as is labelling it as an ad-only company.
My point being, their capital structure is focused around the IP they own which is mostly tech stuff rather than ad stuff. When they don't build the stack themselves they acquire it, not merely purchase products, like some tv/radio network would do to create content and broadcast it. On the other hand when they spend on improving their ad monetization it's an expense, not an investment, which to me kind of proves my point.
Tech is certainly something Google puts a lot of investment into, but it isn't the company's primary focus or interest.
Yep, it's a tech company.