If Meng Hao did not eliminate him, the other six men would have found it strange. That, in turn, could have given birth to other problems.
Although Meng Hao had not been a part of the Cultivation World for a very long time, he had experienced many things in the past six years. He was not the soft-hearted scholar he once had been. When killing became necessary, he did it without hesitation.
Enmity had been created two years ago when the man had attacked him, and then had his Spirit Snake killed. The man was of the ninth level of Qi Condensation, so it was impossible to tell whether or not he would reach Foundation Establishment. Killing him now would prevent any future troubles.
From the incident with Ding Xin, Meng Hao had learned that even when attacking enemies weaker than yourself, you must be quick and thorough in the kill.
From the incident with Wang Tengfei, he had learned that even an opponent with a lower Cultivation base could harbor resentment, and pursue vengeance ruthlessly.
In these six years, Meng Hao had matured, both in his personality and in his methods of dealing with matters.