Tyr's surprise at seeing Fenrir was genuine, the god was not someone who felt the need to shield his emotions, despite being private about himself and such. His eyebrows rose and the same conflict Fenrir had felt before was visible in his eyes. The confusion on what to do. (What not to do.)
His instinct told him not to rush into the situation, but to watch, he had given Fenrir no provocation- no need to snap off his other hand. On the other hand, Fenrir had been speaking to Loki and that sent Tyr's inner alarm bells off. (How long to Ragnarok now?)
Human shaped or not, Fenrir was unmistakable to Tyr, though he had the urge to try and groom the wolf a little - at least in his human form- something more presentable and less likely to send people running for the police. (Not the kind of attention one wanted.)
The approach was cautious, but once he was close, the god lifted his hand - the one Fenrir had bitten off, plus he was still taller - to ruffle Fenrir's hair, mussing it more. His hand twitched, a painful phantom pain crawling across from the finger to his upper arm and Tyr withdrew the touch, also taking a step back.