My response: No, not if by that your friend means that the shift in investment funds itself is what is driving the stock price up.
What drives any stock's price, and thus all stocks' prices, is the market's assessment of the current value of its future profit stream, discounted for risk and time. If a stock's price goes up, this means that the marginal investor expects the firm's profits per unit risk to rise. It can be due to either firm-specific developments or to economy-wide developments which affect the firm's revenues, costs, or risks.
Just because there is "more money invested" does not mean that stock prices will rise -- the act of choosing to buy a stock does not make the management of the company smarter, or its production processes better, or its cash flows less risky. But the belief by the market that the company is smarter, more efficient, or less risky will, when investors trade on that belief, cause its stock price to rise.
Think about this issue at the level of the individual transaction: what would make you willing to pay $10 for a share of XYZ, Inc. instead of $9? If you believed that you would get a higher return on your investment, even after paying a higher price. You see higher profits per unit risk in the future of this company, or you follow the investment strategy of someone who expects good things of this company. It is the forecast of higher cash flows and/or lower risks that generates the demand and encourages investment, not the size of the pile of money being invested.
Better? Or still too subtle?