I also think it is too early especially when we are going to receive snow and ice in my area any time now. I thought we are supposed to plant tulips, hyacinth, and spring flowers in the early months of April and May.
I think that may be too early also. The bulbs usually do well once they don't start to rot or be affected by any insects and so on. But I'm thinking that they may come up too early when the weather is not good for tulips. They love lots of sunshine and warm temperatures so if they shoot out too early the cold weather might be really bad for them.
Here in the South people plant their tulips and any other type of bulb plants in November and December, so it doesn't seem strange to me that your neighbor would be planting them now. However, I did notice that you live in New York and I can understand your question and concern about planting spring flowers so early. However, you did say, the neighbors garden is beautiful every year, so they must be on to something. Go over and talk to your neighbor to find out why they plant their tulips in December. Remember gardening is a very social learning activity and this is a wonderful opportunity to learn from your neighbor.
My understanding of bulbs is, you plant them in the cool weather during this dormancy period, and they'll store all the food and water they need for winter, and use the food and water slowly during this time because the plant is actually saving for the spring. When temperatures start to warm up on a more consistent basis the plants will begin to grow and eventually bloom.