To answer your question, though, when we see strong calcium lines in a meteor spectrum, it's typically coming from the calcium H and K lines which are very short wavelength, making them look quite blue/purple. These are different lines than you see when doing a flame test.

And some are sodium-rich, while others are iron-poor. Also, the oxygen/nitrogen is from the atmosphere, and we seen it, with increasing strength, at speeds > 25 km/s. There are many different compositions that we see, when observing meteor spectra, and it's not nearly as simple as the image suggest.

It's worth noting that most meteors will be composed of many different elements. So, you will typically see iron lines along with sodium and magnesium. Some are mostly iron, and you will then see just the iron 'multiplets' that are towards the blue/green end of the spectrum.