Below is copy pasted from above website. In any case, share prices fluctuate a lot, due to many factors. And every time, someone writes an article about it, but it never means anything.

Misconceptions About Market Caps Although it is used often to describe a company, market cap does not measure the equity value of a company. Only a thorough analysis of a company's fundamentals can do that. It is inadequate to value a company because the market price on which it is based does not necessarily reflect how much a piece of the business is worth. Shares are often over- or undervalued by the market, meaning the market price determines only how much the market is willing to pay for its shares.

Although it measures the cost of buying all of a company's shares, the market cap does not determine the amount the company would cost to acquire in a merger transaction. A better method of calculating the price of acquiring a business outright is the enterprise value.