In a careful reading of his encounter, there are various different reactions that Tom displays, all changing pretty rapidly as their conversation progresses. When the devil first speaks, Tom is "exceedingly surprised, having seen nor heard anyone approach," so, the devil catches him off guard and startles him a bit. Then, as he studies the devil, Tom becomes "perplexed" because he is dark, but not like any man he had ever seen, and was dressed strangely.
The devil then accuses him of trespassing, and Tom's reaction turns to one of fearlessness and mocking as he tries to correct the devil, saying the land belonged to "Deacon Peabody." Tom continues to be unimpressed and confident, even after the devil claims he killed Peabody and owns the land. He demands to know who the devil is, and "what right" he had to the land. Tom is arrogant and confident, and a bit offended by the devil's assertions of power. He is unimpressed. As the chat longer, the best description that can be found to describe Tom's reaction is this:
"One would think that to meet with such a singular personage in this wild lonely place, would have shaken any man's nerves: but Tom was a hard-minded fellow, not easily daunted, and he had lived so long with a termagant wife, that he did not even fear the devil."
That sums it up pretty nicely--Tom's wife was so horrendous that the devil didn't scare him, and he was pretty solid and stoic in nature, so he wasn't really bothered. It is an interesting reaction, and pretty amusing. Anyone else would have probably been scared out of their wits, and terrified, if the prince of darkness had shown up out of nowhere and told of all of his awful deeds. But, Tom took it in stride, and behaved like it was just another normal day. I hope that helped; good luck!