Frankly, this conduct from Tkachuk is rather surprising. He has earned a reputation as a tenacious competitor in the league. The slight contact from the barely discernible tap on his skate should not have elicited such a response from him. It's a bit embarrassing, to be completely honest.
Although Holl was indeed caught unprepared and reaching in the play, the contact with Tkachuk's skate was hardly perceptible. If the officials were determined to penalize Holl, they could have chosen to call both players – Holl for tripping and Tkachuk for embellishment. Nonetheless, we must bear in mind that these are NHL officials, who are not exactly renowned for their impartial decision-making.