Hmmm. If you're talking about the common foxglove, digitalis purpurea, they are most often biennials, i.e. germinate in one season, flower the next, shed their seed and pass on making way for the next generation.
I guess it's possible that a baby was growing near the same site last year, and that one has white flowers.
All the foxgloves iin my garden are self seeded, and they vary in colour from the common mauve, through pink, cream and white (all on different plants I must say). Some have the excelsior gene from some I sowed yonks ago, so they have flowers all round the flowering stem, not on one side. The bees do their bit pollinating them all, so next years crop is a bit of a mix 'n' match. I can make a pretty good guess as to what colour next year's will be by looking at the petioles - a dusky pink suggest mauve, a paler colour suggests white - but that's not 100% accurate when it comes to flowering time.
So I'd suggest that a pollinated seed fell from the mother plant last year, which had been pollinated from another plant, grew in pretty much the same place but had a different genetic blueprint.
And if you want them to spread around your garden, what I do is leave the flowering stem until seed has set, cut it off and whang it round the garden - in fact, a bit like waving a magic wand.