One month ago, rising tech star Pinterest (NYSE:PINS) provided investors with a preview of its first-quarter earnings: "Pinterest preliminarily expects revenue for the quarter ended March 31, 2020 in the range of $269 million to $272 million." Global monthly active users (MAUs) was expected to fall in the range of 365 million to 367 million. 

Investors cheered the news, bidding up Pinterest 12% initially, then continuing to bid up the shares over the days and weeks to come. But after a month of such gains, Pinterest finally announced its official numbers on May 5: The company maxed out its projected sales range ($272 million in revenue) and maxed out its user base as well (367 million). 

And investors sold the stock anyway.

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Image source: Getty Images.

The day after the release, Pinterest stock sank 15%. Why? Perhaps it was because of what Pinterest did not say in its preview of earnings but did reveal in the actual announcement.

Despite growing MAUs 26% and sales 35% year over year in the first quarter, and despite reporting "record levels of engagement globally (in impressions, searches, saves, board creation and visitation)," Pinterest still failed to earn a penny's worth of profit in the quarter -- instead more than tripling its GAAP losses to $141.2 million. 

If that was investors' reason for selling, though, it may be a mistake. Pinterest's GAAP result was weak, true. But the company grew operating cash flow 73% and despite roughly doubling capital expenditures generated positive free cash flow of over $50 million. This 71% increase in cash flow for the quarter was nearly enough to erase the preceding three quarters of cash burn.

Pinterest may not be a money-printing monster stock yet, but it's on the right track to getting there.