The value of every investment plays a role in determining the ultimate value of the investor (Alphabet in your example). Lets take a step back and review what the market is doing on a daily basis when you see stock price moves. Each buyer is essentially making a bet on what they think the company's financial statements are going to look like over a couple of quarters or years (duration depends on the type of company i.e. mature or growth).
So the answer to your question really is...unfortunately...it depends. Using your example, if Alphabet (~$870bn mkt cap) buys 1% stock in Tesla ($135bn mkt cap), without doing any math we can quickly surmise that the investment would be too insignificant relative to Alphabet's entire business to drive any attributable stock price moves.
However, if Alphabet buys a 10% stake worth $13.5bn, what happens? Lets assume Tesla rises 30% the next day (which would be a huge move), the impact of that move on Alphabet's holdings would approx +$4bn which is less than 0.5% of Alphabet's mkt cap, and too small to try to establish any causal relationship with Alphabet's price moves.
If we keep repeating the above calculation with higher levels of ownership, or even a different company with a higher market cap, you'll get higher impact to the investing company until, maybe you're able to say, the move (x) in this company (Tesla), is responsible for a portion of the move (y) in the other company (Alphabet).
However, I would argue, that unless a company's primary business is investing in other businesses, or it makes a small investment in a company that ends up becoming a publicly traded behemoth (happened to Yahoo and Softbank holding Alibaba shares) the above should not happen. Shareholders invest in companies with a somewhat well defined business mandate, not to turn around and invest in other public companies unless it is for a strategic purpose (in which case the daily moves should be secondary to the business execution/growth story).
If you think about it critically, it is a highly inefficient use of capital for one public company to invest in another. The shareholders perspective absent a strategic investment rationale, sounds like - If I want to be long Tesla, I would rather do it myself than hand my money over to Alphabet to do it for me. At the point one company's investments in another public company begins causing attributable daily moves, I would argue as a shareholder that the holding needs to be divested to streamline the business and give me a clearer view of my investing risk.
Furthermore, trying to calculate this type of attribution is a bit futile. In the examples above, we're taking a very simplistic view of the investing company's portfolio, and yet moves are not easily attributable to specific investing activities. When you then consider that Alphabet might have 1% of Tesla, 2% Company B, 3% of Company C and they're all moving in different directions on any given day, in addition to lots of other opposing factors - Wall Street loves management, but an anti-tech bill just passed on the same day Alphabet won a massive govt DoD contract, spun off one business for a massive profit and wrote off all investment in a failed business line..... you would realize that it is never that simple.