The fungus will not harm the plant, so don't be alarmed. Although, fungi need cool, damp, moist conditions to thrive, they also need spores to develop. Although it is possible that spores came in by air current, it is far more likely that the spores were in the soil. If you added some soil yourself, then that soil is probably contaminated with fungus spores.
You were right to remove the fungus and the surrounding soil. In fact, I suggest you scrape off all loose soil not directly in contact with the roots. This may help remove other spores and it will also hasten the drying out process and increase the air circulation. Try to provide lots of bright indirect light and warmer temps, if possible.
Let me know of you have any questions.
Will Creed
wcreed@HorticulturalHelp.comMy website