Magnesium is different than titanium. It autoignites in air at 473°C. Titanium burns in air at over 610°C. That's a pretty big difference. Both burn in pure nitrogen (forming a nitride and not an oxide), making flames hard to extinquish. Which is why Mg was used in incendiary devices in WW2 and in other conflicts.

The allusion to checking sparks on a grinder refers to an old and effective shopcraft method: different metals have different spark patterns when applied to a grinding wheel. Another way to check whether your pedal spindles are really Ti is to take it to a junkyard with a box of donuts. Tell the guy that you'll give him a box of donuts if he "shoots" your spindle to confirm that its Ti. He'll use an X-ray Fluorescence Spectrometer to tell you the Ti and alloy composition.

Agree, pure Ti would not be a very good metal for this purpose - not as strong as the alloy.