If this had been an April Fool's thing, it would have just given someone the idea to test it out.
The concept is very real; the premise behind it is actually the reason some applications are buggy: it's up to the application to set/reset memory contents before reading from a given location, as an OS (or in this case a driver) tends to only worry about allocation of memory and making sure nothing steps outside those memory bounds. Otherwise, there's no care for the contents of said memory, and an app that doesn't reset memory contents can easily get old data that otherwise was never cleared out. There may be some mechanisms to prevent apps from using memory that's been recently allocated to another program (for performance reasons if nothing else), and memory segmentation makes it hard to get huge chunks of data in some cases, but the data is still there.
It doesn't hurt that memory is designed to remember for as long as it can.