Hi Peter. As you say, it's good to keep tabs on anything if there's a chance that it's of concern. In this case, I expect that 'spontaneous' means that the bulbs lay unnoticed in a section of the property where they were planted a long time ago, and then reappeared as usual (as opposed to having spread to the spot). It's quite common that people are surprised by its appearance at this time of year - especially because the flowers precede the foliage, and it will often skip a couple of years in flowering.